Just a few thoughts on that topic:
Yes, a sane German leadership would have never started that war, the holocast and a lot of other very bad things. However, they did what they did and were a bunch of insane, drug addicted megalomaniacs. There was no way they would have chosen a different path.
There were a lot of plots an assassination attempts against Hitler, but somehow he survived all of them. For example: Georg Elsner build a bomb inside the Bürgerbräukeller (a place were the Nazis held a lot of speeches) and Hitler survived just because he left early. Another attempt failed, because the acidtrigger for a bomb on a plane he took to the eastern fron, had frozen in flight.
There is a nice listhere.
I don't remember the source, but I have heard somewhere that the USA could have had 3 additional bombs ready till the end of 1945. not sure if that is true.
You should however not forgett that the Germans had a few tricks ready at that time and if we assume that they had won the war against the UDSSR and the UK, there would have been even more. Maybe not nuclear weapons, but other advanced stuff like the Jetfighter/bomber, guided missiles, early ICBMs (A9/A10), etc...
Not sure what kind of impact that would have had on an US attack against Germany, but I will try that out in my next HoI3 game.

Well, one more, slightly on topic question: What would the Loroi think about this part of the human history?