I hope somebody finds life underground on Mars.

He is probably right about civilization destroying itself, or at least thinning itself out. I think if/when a nuclear bomb gets dropped, the devastation will be horrific, sufficient to brink all countries of the world into some sort of verifiable agreement.

I think he missed a possible cause of human extinction:

"Billionaire entrepreneur Elon Musk, physicist Stephen Hawking and other tech luminaries have signed an open letter warning against the dangers of starting a global arms race of artificial intelligence (AI) technology unless the United Nations supports a ban on weapons that humans "have no meaningful control over."

Killer robots are still my best guess.