Running a government requires a lot of cash flow. I think its sort of inevitable that it's going to need to start coming mostly from the later and not the former.
There is growth, it might not be where you are, or it might be superimposed with other effects for you.
https://en.wikipedia.org/wiki/File:Total_population_living_i...
* via government subsidies
Why presume that "running a government" is inevitable at all? How much longer do we think these states of old are going to putter on for?
Nature abhors a vacuum and that principle extends to power vacuums.
But there are plenty of ways (and plenty more each day) in which human and AI collaboration can fill power vacuums that don't require pseudo-sovereignty over huge landmasses or monopolies on the legitimate initiation of violence.