Some humans will be rich and they'll buy things. For example those humans who own AI or fabs. And those humans, who serve to them (assuming that there will be services not replaced by AI, for example prostitution), will also buy things.

If 99.99% of other humans will become poor and eventually die, it certainly will change economy a lot.

That’s assuming a large chunk of humanity will just lay down and die off.

The 99% of humans will band together and destroy the ones who "own" things.