I was once writing a timeline based on this premise, but I abandoned it before posting for... some reason.
Anyway, my proposals were:
-some civil war among the Ottomans concerning succession after Murad; this allows Christian forces to capitalize on their victory and take part of Ottoman holdings in Europe
-breaking off between Poland and Lithuania; at the time of Battle of Varna Lithuania was ruled by Casimir Jagiellonczyk, brother to Vladislav almost independently. I think that surviving Vladislav would lead towards end of an union and creation of independent Kingdom of Lithuania, in conflict with Muscovy and Poland
-perhaps a more lasting union between Poland and Hungary
-creation of independent kingdom of Bulgaria under Hunyady as king (that was his supposed to be his reward in the event of successful war). I also think that he would be in a good position to gain later possession of Constantinopole after Constantine (?)- perhaps we could see the Empire based on Thracian and some greek lands?
-Poland takes possession of the entire Prussia in early 1450s - with a successful Crusader King, known for vanquishing Ottomans there is little chance that Teutonic Knights could recruit mercernaries with just promises, as they did in OTL 13-year war. Perhaps Vladislav would relocate the order to Black Sea, maybe Crimea? (Teutonic Cossacks?

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