We've replaced human jobs in the past not just made them more efficient. Horses (and all the jobs to do with them) were completely displaced by cars. Those jobs aren't more efficient, they're gone. Similar with many other jobs during the industrial revolution.

This is not a zero sum game. For an economy to exist we need consumers. For consumers to exist we need people to have jobs and be paid. So the equilibrium is that there will be some new jobs somewhere, not done by robots, that will pay people enough to consume the (better and cheaper) goods made by those robots. Or we'll just have a lot of leisure time and get paid by the government. Or (like some other discussion thread) we'll all be wiped out or slaves in the salt mines if the elites can just sustain/improve without us and are able to enforce it. Either way, it's not the scenario where we're out of jobs sitting at home.