Ah, but we do have Linux. And it can survive without Linus, if needed. In fact, it must survive. He's 48 now. What do we do in 50 years? Do we assume something else is going to come along that's so awesome that Linux becomes obsolete and gets abandoned? I don't think that's a good assumption. A better assumption is that computers are now stable tech, like internal combustion engines, and that Linux is the best OS we have, and could be around for centuries. Which is an amazing legacy for him, but... it's going to be a legacy, sooner or later.
And what if he has a heart attack tomorrow? I just lost a friend to a heart attack this week. Not much older than Linus, and in great health. It happens. Do we just give up, or does Linux go on without him?