By the end of the war, Hitler was - to put it bluntly - insane, to a large part due to drug abuse. He would have had to be replaced because he was no longer competent to run a state.

There's a longer story here, involving among other things an incompetent doctor. I would not be surprised if the overall course of the war was affected by Hitler's insanity, but I don't know to what degree that's true.