I've got a creative writing degree mate. Believe me, I can think of a million different scenarios if I wanted to.

I can just tell where plausibility ends and fiction begins.

The fact is that nuclear weapons exist, along with governments that would rather have power than a bunch of rich psychopaths.

There is no functional collection of rich people who are actively pursuing the eradication of even half of humanity, Thanos Style, who could aquire the means to do so before the United States or China could.

They don't have an auto sense for like mindedness, and while they have a disproportionate amount of madmen amongst them, most rich people are just selfish assholes, not genocidal monsters.

It's like expecting a high-school bully who steals your lunch money and breaks your toys to grab an AK47 and start mowing down people the moment they graduate.

It'll just be more of the same, writ large, at worst.

They aren't nearly creative enough, or motivated enough, to end the world.