I recently read that the idea that WW1 was inevitable due to arms races and the like is spurious because the same conditions existed in the Cold War for 40 years without resulting in WW3.
So if that reasoning has merit then if we take away the particular spark then WW1 as we know it doesn't occur. So stop Princip in one way or another from killing Franz Ferdinand.
The only reason we didn't have WWIII was nukes.