About half a dozen of US Congressmen are foreign born. What if the sole survivor is Rep. Lincoln Diaz Balart, for example. He can elect himself speaker as long as he wants, he'll never be President. Of course, if Diaz Balart and Mel Martinez are the sole two survivors, they might pass a constitutional amendment to make themselves eligible.
They can pass constitiional amendments with a surviving Senator, but it still has to be ratified.
Well yes, but that would happen swiftly I reckon. In that extreme scenario. It might help if the remaining term wasn't long.