that's called post scarcity. The thing is, their labor (if needed at all at that point) will create massive amounts of resources. Millions of times more than today. Unlike capitalism they will not be dependant on the owners of the robots for a job, and can live freely without needing to do any labor (instead of the starving which would happen under capitalism).

This is the ultimate goal of socialism. Capitalism puts it off because they know the starving workers will revolt.

"what happens when hypothetically everything is done by robots and the generations after generations over thousands years who made us to this point (that everything is done by robots) are all dead and there's no way to reward them?"

I think you are assuming the people who built the machines that automate stuff will be paid all that it produces. Nobody can consume that much and as shown in the soviet union and many other instances, people invent to invent not for money. The inventor may get extra resources of course, nobody is barred from giving.

That actually outlines my understanding of the difference between Proudhonian and more leftist economic thought. Although both mutualist-anarchists and marxists do agree on the destruction of private property.