By what mechanism, exactly do you think this will happen? He has no plans to sell. He'd like to go to Mars himself, but not if he doesn't think the mission of SpaceX would continue without him. So...that leaves it becoming 'a nationalised company of the US Federal Government"....aka, the gov't takes it over by force? How likely do you really think that is? It only took over Ford because they were bankrupt, so all he needs to worry about is not going bankrupt, which I'm sure he's thought of already.