Simply put: WI Tito had been killed during WWII? What would be the effect post-WWII and how would it affect the European balances of power?
I think the two main questions should be:
1)when does he die (early in the war or towards the end)?
2)who takes over?
During the war, Yugoslav partisans tied up numerous German troops from being able to fight elsewhere in Europe, but this was mainly due to Tito's leadership. Post-war, chances are Stalin would send in troops to make Yugoslavia a Russian satellite like he did with most of Eastern Europe. Once the Soviets pull out, the country would probably disintegrate faster than it did OTL.