You can't have an economy with just AIs because they don't consume anything except compute. If AI can build more compute, they can definitely defend their owners.

There's a limit to how much elites can consume. Most people are happy with a few million dollars or something. The people who go past that are obsessed; they're competing with each other.

There is no reason for elites to secede. There is no reason why we can't have bajillionaires and subsistence farmers on the same planet, in the same economy, using the same dollars. (It's basically already happened. What's a few more zeroes?) If AI cannot provide security (either directly or through creating wealth used to buy security) then it will not create this level of inequality in the first place.

Places like Sudan have already been left behind and they're currently in the middle of a very bloody war which the West is largely ignoring. Now the Western middle class is making noises about violence because their prosperity is under threat. But this is what capitalism has always done. This is what we signed up for.