It sounds like these nameless oligarchs are providing a lot of highly paid work for a lot of skilled workers, so good for them. The workers know all the secrets of the bolt holes by the way, since they built them and maintain them, so the oligarchs might have some unwanted company when they lock themselves in. No fortress is impervious to human attack, and the people left on the outside will have access to heavy equipment. Just dig under their bunker and roll it over and see how they like that. Find the vent and pour a fifty gallon drum of bleach down there and I bet you will be seeing them soon. If the super rich are smart they will just buy a fast yacht with a huge fuel tank. Hell, fill the swimming pool with diesel fuel or canned ravioli. But if there is an engine failure, bad storm or a pirate attack, they are on their own. At some point they will be drinking urine just like the explorers of old, and wouldn't we be sad about that.