Here comes the flame war!
Anyway though, if Deir Yassin hadn't happened, almost nothing within the broader war would have changed. There were already dozens of massacres and forced uprootings that occurred throughout the '48 War on both sides, one more or one less wouldn't change much. What is might change though is early Israeli domestic politics. The fact that the Irgun committed such an obvious and heinous crime publicly discredited them somewhat, and made Ben-Gurion's job in disarming them later much easier. If that hadn't happened, the Irgun and the Revisionist movement might have been stronger in early Israeli politics. That could lead to a more aggressive foreign policy, or a more discriminatory policy towards Israeli Arabs in the 1950s (ethnic cleansing instead of military rule, for example).