If AI replaces workers, we wouldn't have an economy. It would probably be the end of capitalism. Or at least the end of the consumerism driven capitalism that we have known since the end of WWII. I don't know what would follow but it probably wouldn't be pretty. Honestly at that point, I could see the end of humanity. If truly we get to the point that machine intelligence is more capable and people are entirely marginalized then it's game over. At best a few human specimen end up on display in zoos, but maybe machines might not even have any use for zoos, since they can just share "experience" digitally.