It's kind of like their own punishment. They'll laugh as they descend into their bunkers, thinking "no one can get in!" Not knowing that the exits will be boarded up.

At last, one of them will emerge, after having ate the other occupants - children included - and they will be met by a crowd of brown people (global warming caused "white genocide").

The crowd will then drag the surviving billionaire to a down square, where they'll be submerged into a vat of liquid metal, forming a statue with a horrid look on it's face, to be mounted on a block with a placard titled "The Last Billionaire".