I don't think Eliezer Yudkowsky or Luke Muehlhauser would lead significantly different lifes if there were no existential risks. They are just the kind of people who enjoy doing what they do.

I think at one point Eliezer said that, if not for AGI/FAI/singularity stuff, he would probably be a sci-fi writer. Luke explicitly said that when he found out about x-risks he realized that he had to change his life completely.