You must realise that if you were to eliminate the people responsible for most of the world's discoveries and events, someone else would do them instead. The environment that allowed Hitler to come to power would easily produce any number of men like him, and they may well be more competent. And if it hadn't happened in Germany, it most certainly would have happened in Britain or another Allied power.
As for scientific discoveries, they may take a little longer, but not much longer. Science had already advanced to the point were nuclear physics were known of and being studied, and practical applications we becoming possible. There were also, and there are and were with most discoveries, other teams worldwide doing the same research.
You need to be very well versed in history to predict what events were truly unprecedented and could alone have altered human history, and even then its not something you can predict with confidence. And then Chaos complicates things further. The fact is, the effects of some events diminish with time, while others grow phenomenally. In fact, most events probably have many effects of both types.
__________________
| (• ◡•)| (❍ᴥ❍ʋ)
|