Fascism needs an enemy to rationalize its own politics. Hitler's state of mind and well being would've been irrelevant. The legitimacy of the entire regime was at stake.
Adolph Hitler, as an individual, did not need to exist for any of the 20th century to unfold the way it did. If Hitler dies on the battlefield in WWI that conflict still devastates Europe, the ascending, world-wide labor movement would still largely have been crushed, widespread banking failures in the 20s and 30s would still give us the great depression, the radical movements of the 30s would still have formed, and the revanchists would still have formed their fascist parties in response.
No matter what they would've called themselves or who led them, something just like Hitler's Nazi party would've come to power in Germany. The exact circumstances might not have been the same but war in Europe was inevitable as the existing power structures were losing their legitimacy and either being voted out like in Spain or overthrown, like in Russia.
This is not meant as a slight to the poster I'm replying to, but I think that great man theories of history are mostly bunk. Historical materialism is far more useful of a lens because even in a world without Hitler all the institutions which brought him to power would still exist.