It's not like we don't deserve it.

I doubt anything will get us all.. But with increasing squalor from overpopulation I suspect a virulent pandemic of some sort will wittle us down… Total nuclear war & nuclear winter could be ‘our answer’ to global warming.. But baring the current US administration, the powers that be know better than that. Limited, definitely; total, no.

I’ve come to feel when prominent apolitical types give such dire predictions it’s more to focus and challenge us to avoid it than their actual heart-felt expectation ~

cut the population big time

I think he is wrong, I think we are in for a fall and massive depopulation, I doubt we will completely wipe ourselves out at least not all at once, civilization will fall likely never to return.

As far as I know Hawking said something similar to that with regard to general Artificial Intelligence, and as an AI expert I would respond that this prediction is utter nonsense.
On the other hand there are many other ways of how mankind can fuck up its future and indeed mankind has been working hard to already do that: climate change from burning fossils fuels, destroying valuable eco-systems, causes the greatest mass extinction of species for millions of years, polluting the environment, and creating enough weapons of mass murder to wipe out the whole planet being only some of them.
If mankind does not stop messing up, I am not too optimistic about those 100 years, but it will be a bit different from "not lasting beyond". It will probably be uglier, with millions of people suffering and dying a large part of mankind getting involved in war and conflict and a slow and long reduction of the number of humans on this planet in an ever more hostile and less life-supporting environment. There may be some kind of rebound eventually or not.