I don't think this calculation works out, actually. If you're purely selfish (don't care about others at all), and the question is whether to devote your whole life to developing FAI, then it's not enough to believe that the risk is high (say, 10%). You also need to believe that you can make a large impact. Most people probably wouldn't agree to surrender all their welfare just to reduce the risk to themselves from 10% to 9.99%, and realistically their sacrifice won't have much more impact than that, because it's hard to influence the whole world.