Now maybe if it happened back in '32...
even in 32, because i think the nazi party was more than hitler. they had himmler, goering, and most important, the genius of propaganda goebbels.
a hitler killed in 32, would be a hitler martir, for the nazis. a re-born aryan god, sitting a side with odin, thor and wotan, following the ethnical/cultural/national "salad" of nazi ideology.
a hitler killed in 32, would means also a more eficient german warmachine. since the nazi leader of ww2 would have the good-sence to dont intervent over military issues, as hitler did many times and did wrong, for the lucky of england and ussr specially.
i think the answer to avoid the ww2 was the allies should adopt more strong positions against germany when they started to build their weapons, instead what really happened, that nazis used the weakness of western political positions as them strong.
wasnt churchill that said the peacemakers are usually the ones who throw meat to the lion, expecting they would be the last to be eaten ? england and france should be strong at the time when german warmachine was just in papers.
of course churchill did a little bit the same(throw meat to the lion) with soviet union, closing the eyes for the invasions, of poland, baltic states and finland, but at that time was a matter of surviving isnt ?
and also stalin did the same with germans, triyng to be the last to be eaten by the german lion. when ribbentropp-molotov treaty was signed, the future of poland was defined, by hitler and stalin. even if england and france adopted more bolder actions at that time, after the treaty signed and before the polish invasion, allies would had some chance to decrease the time of war. but in 39, the german warfare and their thatics was already the most modern of the world.