It’s hilarious to me that there are people that think just a few people will control everything and the rest of the population will just accept whatever handouts they get. It’s like they’ve ignored all of human history.
For the first time in human history, military power doesn't require advantage in numbers. The rich will simply build an artificial army and use it to control everything. Kinda like Mr House from Fallout New Vegas.
Drones aren't terribly expensive these days, and an "artificial army" requires a long production pipeline even if parts are printed.
I reckon the hypothetical plutocracy wouldn't want to live immediately next to the land they stripmine or otherwise experience the environmental consequences they would wish to ignore, thus it would be difficult for their supply lines to be fully encapsulated.
Alternatively, the hypothetical plutocrats could engage in trade with the people they attempt to wall off, become better off than autarky, and ideally approach some of the better systems that exist today.
It must be awful tempting for dictators to steal the commanding heights of the economy -- we see it happen so often -- and little do they realize the prosperous world they want comes when these institutions they steal are protected, enforced, and respected.