As with any highly risky enterprise, I think he should be increasing his odds by raising one or more prodigies of his own, that would be able to carry on with his work, if he himself wasn't able to.
He does have 5 children. :-)
László Polgár had a thesis that one does simply raise a prodigy and managed to do pretty well on that score, given that he and his wife Klára proceeded to then raise three female chess prodigies.
Of course one swallow does not a summer make, so it could just be blind luck, but it is an interesting and fairly persuasive case.
Like in Judit Polgár's development; if a child was trained in a subject early on and provided the right opportunities, then "genius" can be developed. When I have kids, my plan won't be to focus extensively on one subject (like chess), but on several subjects, including Esperanto like Judit Polgár was taught.
http://www.amazon.com/books/dp/0910707561 is a good source of insight based on it. However I would humbly suggest that consciously attempting to follow some of its advice would be legally actionable.
Of the people alive today, I suspect Elon is probably one of the few who will be widely remembered a thousand years from now.
Perhaps most of all by the inhabitants of Mars.
NB I freely admit it having a romantic fascination with the colonization of Mars after reading Kim Stanley Robinson's Mars trilogy and Robert Zubrin's The Case for Mars:
http://en.wikipedia.org/wiki/Mars_trilogy
http://en.wikipedia.org/wiki/The_Case_for_Mars