The collapse of civilization is what drives the unwarranted belief in Nick Bostrom’s simulation model - Elon Musk has said that for himself, personally. I too believe that future isn’t good but I don’t believe in the simulation assumption argument. What I believe in and why, is documented, with 109 references, in my paper response to Eliott Edge’s pro-simulation article on this site -
Not sure about the connection between existential risks and Bostrom’s simulation argument. But I do agree of course that we can’t predict the future and don’t know if we’ll go extinct or survive and flourish. Obviously things could go either way.