That is right. Eventually you will run out of rich people to buy what the poor people built. And you will be left with a bunch of..............
I get confused at that point about what happens, something like recession, or repression or whatever. But when you run out of rich people, what will the poor people build then? hmm, I dunno, maybe cheaper stuff for poorer people. Or, maybe they will have to go back to making their own stuff! Like they should have been doing in the first place.