Which humanity-ending theory seems most plausible?

The simulation idea is possible to imagine, but there is no clear way to test it or estimate how likely it is. A claim that an outside entity could end everything can fit almost any outcome, which makes it hard to compare with explanations that at least have observable mechanisms.

I’d separate “what could happen?” from “what do we have reason to expect?” The first has endless possibilities. The second needs evidence, and speculation alone does not give us a ranking.

I’d start by asking whether “the end of humanity” means extinction or a collapse of the world people know. Those are very different claims. A disaster might badly disrupt civilization without wiping out every human, so broad catastrophe theories shouldn’t automatically be treated as extinction predictions.

For a grounded discussion, compare proposed risks by whether there’s a plausible mechanism and whether anything could reduce the danger. A simulation being shut down is much harder to evaluate that way, so I’d call it an intriguing idea, not the likeliest answer.