Ok, first some rough overview of situation, not known by a lot of Western folks. Nationalism rose in '80es because of declining economy. Also because crimes of all armed groups in WWII had been swept under the rug and ignored. Croatian Ustasche did a horrifying and brutal genocide against Serbs, Jews and Gypsies. Albanians SS brigade supported by Italian Albania did their ethnic cleansing act on Kosovo and in Macedonia. And Serbs had to repay the favor by "pro-King" and "anti Nazi" Chetniks being most active in Bosnia and Montenegro, killing non Serbs and alleged communist supporters. There are rumors they attacked Germans occasionally 
Than the "liberation" came in 1944. and Partisans did their own measure of justice (and all justice must come from a barrel of a rifle or gallows)
And when situation stabilized by early '50es... it was ALL swept under the rug, to be happily ignored in the goal of building "Brotherhood and Unity". People mostly accommodated to the new situation, most had their living standards greatly improved by '60es... though both Serb and Croat nationalist emigration existed abroad, busy keeping old hatreds alive.
Economy was heavily dependent on foreign aid, still not that much. Still, with Oil Crisis of '70es country's debt increased, to the point that after Tito's death "Collective Presidency" and its economic organs had to obey to IMF recommendations on how to run economy in order to repay debts. Now, those recommendations weren’t that healthy for the country, and furthermore were being implemented by leadership that was (by early '80es) already very corrupt and keen on finding new ways to get state money in their pockets, advancing their own positions and supporting power climb of their friends and partners in theft.
By late ‘80es economy was hitting rock bottom, not quite the penniless state USSR found itself in 1990. but bad. Inflation and unemployment were worse since ever from ‘50es onwards. And with Moderate increase in speech freedoms and tolerance nationalism was on the slow rise since after Tito died, with it greatly steeping up in late ‘80es. To worsen everything, its was communist policy during most of Tito’s period to keep police force and state security in one republic, to be dominated by nationalities from other republics, “to balance everything out”. And that sown a lot of hatred. In Serbia everyone was blaming Croats and Slovenians in party and state sec leadership for… well everything. Same, in Slovenia and Croatia everyone hated that Serbs and Montenegrins dominated police and army.
And once real multiparty elections were held, everything quickly went to hell. I don’t know what’s the truth I know that everyone here knew that Tudjman was a dangerous pro Fascist nationalist (and he has occasionally quite public praised WWII Independent State of Croatia), that Izebegovic was a Mujahedin supported violent Islamic nationalist… and so on. And in Bosnia and Croatia they hated every single outburst of Serbian nationalism, immediately connecting it to WWII Chetnik massacres.
To prevent disintegration of country, heck even to prevent it being a violent civil war, you have to change a lot of things. So one by one.
In 1970es. Tito cracks down a bit harder on Croat nationalists during Croatian Spring. It simply has to be done, nationalism on all sides has to be countered, and Old Man is only one with authority to do it. In 1971. technocratic “liberals” are not cracked down as hard as in OTL, so that economy can be a bit more efficient and durable.
Now a thing at which I will clearly be denounced as Serbian nationalist and rest of my post ignored (if it hasn’t happened already). 1972. constitution doesn’t split Serbia in 3 parts. It was best possible fuel for Serbian nationalists one could have possibly created. Until 1941. Kosovo and Vojvodina were integral parts of Serbia from 1912. and 1918. respectively.
When AVNOJ drafted first constitutions of communist Yugoslavia in 1944. and started drawing borders they were still under Stalin’s influence, and communist tendencies everywhere to prove themselves as “democratic” and “multiethnic multinational” by arbitrary creating new borders, new republics, new autonomous provinces.
Even creation of Kosovo and Vojvodina as autonomous provinces was hard to swallow, but in 1944. and 1945. you said “yes comrade Tito”, or found yourself in a ditch with a bullet in your head. Granting them independence near that of republics in 1972. created outrage and breeding ground for Serbian nationalism.
Now. I cant tell whether it would be better for Tito to die a couple of years earlier or later. If he dies earlier it might just be possible that the nonsensical “collective presidency” manages to figure out a way to work before economy makes it impossible. If Tito dies later, than we might see that there is no time for respect of him and his ideology to die fast enough and completely enough by time communism starts breaking down in 1989. And so nationalism doesn’t get as strong in time for its destructiveness to do its dirty work.
And finally. Personally I consider Milosevic, Tudjman and Izetbegovic all guilty in same amount. At times each of them was a rabid nationalist. With Milosevic furthermore, more of the time just being opportunistic scumbag that will ride that wave of popular opinion to stay in power, whether that sentiment is nationalism or paining frogs blue. Still, Slobo had completely no sense of international politics and PR, no sense of giving moderates their way if it could cost him power. (In 1987. he condemned infamous “Memorandum of Serbian Academy of Arts and Sciences” as nationalistic antisocialist propaganda. In 1989. he was The Promised Leader to all Serb nationalists) Best way to avoid him and prevent his rise to power would for someone to point out to Stambolic that Slobo is a potential backstabbing bastard before 1987. Though again and again, some things I heard make it very difficult for Stambolic to stay in power in Serbia in any timeline. He simply wasn’t corrupt enough (im not saying he was a saint, just that he was quite a bit better than most) to be tolerated by rest of economic and politic leadership of Serbia.
With all of above or just some of them happening. Economy is in somewhat better condition in 1989. Nationalism on all sides a bit lower, causing lower “reciprocal” nationalism by other nationalities. By lack of Milosevic bogeyman it might make Tudjman and Izetbegovic not be able to ride their own waves of nationalism to power, and more moderates take their places. Country is still close to a breaking point both politically and economically, still hopefully good enough that a stabile temporary solutions can be found, maybe moderate confederal model is adopted, or just talked enough about long enough for country to get close to joining European Economic Community.
Than the "liberation" came in 1944. and Partisans did their own measure of justice (and all justice must come from a barrel of a rifle or gallows)
And when situation stabilized by early '50es... it was ALL swept under the rug, to be happily ignored in the goal of building "Brotherhood and Unity". People mostly accommodated to the new situation, most had their living standards greatly improved by '60es... though both Serb and Croat nationalist emigration existed abroad, busy keeping old hatreds alive.
Economy was heavily dependent on foreign aid, still not that much. Still, with Oil Crisis of '70es country's debt increased, to the point that after Tito's death "Collective Presidency" and its economic organs had to obey to IMF recommendations on how to run economy in order to repay debts. Now, those recommendations weren’t that healthy for the country, and furthermore were being implemented by leadership that was (by early '80es) already very corrupt and keen on finding new ways to get state money in their pockets, advancing their own positions and supporting power climb of their friends and partners in theft.
By late ‘80es economy was hitting rock bottom, not quite the penniless state USSR found itself in 1990. but bad. Inflation and unemployment were worse since ever from ‘50es onwards. And with Moderate increase in speech freedoms and tolerance nationalism was on the slow rise since after Tito died, with it greatly steeping up in late ‘80es. To worsen everything, its was communist policy during most of Tito’s period to keep police force and state security in one republic, to be dominated by nationalities from other republics, “to balance everything out”. And that sown a lot of hatred. In Serbia everyone was blaming Croats and Slovenians in party and state sec leadership for… well everything. Same, in Slovenia and Croatia everyone hated that Serbs and Montenegrins dominated police and army.
And once real multiparty elections were held, everything quickly went to hell. I don’t know what’s the truth I know that everyone here knew that Tudjman was a dangerous pro Fascist nationalist (and he has occasionally quite public praised WWII Independent State of Croatia), that Izebegovic was a Mujahedin supported violent Islamic nationalist… and so on. And in Bosnia and Croatia they hated every single outburst of Serbian nationalism, immediately connecting it to WWII Chetnik massacres.
To prevent disintegration of country, heck even to prevent it being a violent civil war, you have to change a lot of things. So one by one.
In 1970es. Tito cracks down a bit harder on Croat nationalists during Croatian Spring. It simply has to be done, nationalism on all sides has to be countered, and Old Man is only one with authority to do it. In 1971. technocratic “liberals” are not cracked down as hard as in OTL, so that economy can be a bit more efficient and durable.
Now a thing at which I will clearly be denounced as Serbian nationalist and rest of my post ignored (if it hasn’t happened already). 1972. constitution doesn’t split Serbia in 3 parts. It was best possible fuel for Serbian nationalists one could have possibly created. Until 1941. Kosovo and Vojvodina were integral parts of Serbia from 1912. and 1918. respectively.
When AVNOJ drafted first constitutions of communist Yugoslavia in 1944. and started drawing borders they were still under Stalin’s influence, and communist tendencies everywhere to prove themselves as “democratic” and “multiethnic multinational” by arbitrary creating new borders, new republics, new autonomous provinces.
Even creation of Kosovo and Vojvodina as autonomous provinces was hard to swallow, but in 1944. and 1945. you said “yes comrade Tito”, or found yourself in a ditch with a bullet in your head. Granting them independence near that of republics in 1972. created outrage and breeding ground for Serbian nationalism.
Now. I cant tell whether it would be better for Tito to die a couple of years earlier or later. If he dies earlier it might just be possible that the nonsensical “collective presidency” manages to figure out a way to work before economy makes it impossible. If Tito dies later, than we might see that there is no time for respect of him and his ideology to die fast enough and completely enough by time communism starts breaking down in 1989. And so nationalism doesn’t get as strong in time for its destructiveness to do its dirty work.
And finally. Personally I consider Milosevic, Tudjman and Izetbegovic all guilty in same amount. At times each of them was a rabid nationalist. With Milosevic furthermore, more of the time just being opportunistic scumbag that will ride that wave of popular opinion to stay in power, whether that sentiment is nationalism or paining frogs blue. Still, Slobo had completely no sense of international politics and PR, no sense of giving moderates their way if it could cost him power. (In 1987. he condemned infamous “Memorandum of Serbian Academy of Arts and Sciences” as nationalistic antisocialist propaganda. In 1989. he was The Promised Leader to all Serb nationalists) Best way to avoid him and prevent his rise to power would for someone to point out to Stambolic that Slobo is a potential backstabbing bastard before 1987. Though again and again, some things I heard make it very difficult for Stambolic to stay in power in Serbia in any timeline. He simply wasn’t corrupt enough (im not saying he was a saint, just that he was quite a bit better than most) to be tolerated by rest of economic and politic leadership of Serbia.
With all of above or just some of them happening. Economy is in somewhat better condition in 1989. Nationalism on all sides a bit lower, causing lower “reciprocal” nationalism by other nationalities. By lack of Milosevic bogeyman it might make Tudjman and Izetbegovic not be able to ride their own waves of nationalism to power, and more moderates take their places. Country is still close to a breaking point both politically and economically, still hopefully good enough that a stabile temporary solutions can be found, maybe moderate confederal model is adopted, or just talked enough about long enough for country to get close to joining European Economic Community.