However, this leaves the important jobs to people: jobs that require you to use your head. If we're assuming America doesn't change by the time this happens, we can expect to see a lot of people dying.
But anyway, people will still work, I presume mostly for themselves. Since people will have a lot more leisure time and a lot less work exhaustion, we'll see a spike in intelligence, in which we'll fit the last piece to the puzzle for a post-scarcity economy (hopefully by then, we'll be in a state of post-scarcity anarchism.)I'm still trying to figure out how any of our current economies can apply here. But in any case, I do not believe mining is the end-all solution. There will still be work, it just won't be Taco Bell anymore. People have this weird thing where, when they're not working for someone else, they start working for themselves. I don't know why it happens, but we love to do stuff--that is, when we're not exhausted from doing stuff we don't like to do. Considering a world in which we no longer have to compete for food or shelter (which still rings the overpopulation issue, as a world without starvation and access to medical promotes life), I can see any economic system working, just as long as it's voluntary.
If you've ever seen people make giant murals of their favorite stuff in Minecraft, you're looking into the future. Why do they work? Hell if I know, but they love to do it.
And that all earns money, and Mining can be used to make more money through those things. 