What should happen to the economic system if AI/robots replace most human labor?

AI and robots have become increasingly impressive over the years and some people think there's a chance they could replace large parts, if not most, human labor in the next few decades.

You may or may not believe it, but let's pretend that it's true. What changes, if any, do you think should happen to the economic system if most people became unable to compete with AI and robots?