Honestly, I don't think these guys are in competition with each other for the title of world's richest person--especially Warren Buffett.  I am kind of surprised that Elon Musk is worth that much, but then again I don't really know much about him (yeah, I don't follow the news all that much).

Regarding the retaining of the title: If Musk is worth $23 billion, I don't think he'll have much trouble remaining the richest person on earth.  On the other hand, I don't know a damn thing about what he owns as far as investments, properties, and so forth.  I know about Tesla, but I'm thinking that if he's holding risky assets or if any of his business ventures fail, his wealth could take a big hit.  No idea if that would shave off billions of dollars from it, but I guess it's possible.

And boy, what does a person do after he's declared the richest individual on earth?  I mean where do you go from there?  Lol.  I'd love to have that problem.