Let's say everybody does lose their jobs and is unable to buy goods or services. Is it more likely they will (a) resign to slowly starve or (b) start growing and trading for food amongst each other, providing each other the services they can't get from the robot elite, band together for social protection, etc.?
Shutting someone out from one economy just puts in them in another economy.
Ultimately, even if it costs the unsophisticated people more in time and investment to produce the same goods, the robot elitists don't care about *that* cost, they only care how many of the newly minted Robot Supreme Data Coins the poor humans want in exchange for the same service. That's an arbirtary quantity and the poor humans can always offer a lower bid than the robot automation centers.
But, remember, this whole problem came about because we found such an incredibly cheap and efficient way to produce all our resources. So, even though the humans are going to be forced to trade for what the robot elitists consider virtually nothing, for them it will have vast purchasing power since goods are now so cheap.
In general, I don't think keeping people employed is ever going to be a problem. What the onset of robot workers actually means is that relative income for human workers is increasing to where it is too costly for manufacturing companies to compete for their services compared to the other opportunities they have.
The real problem with super-efficient resource generation is its effect on political dynamics. One person controlling half the economy may be perfectly harmless up to the point where they realize they can use that vast wealth to dictate what laws will be passed. But, who knows, maybe at that point we'll all be so well off that it will actually be harder to buy votes and loyalty than it is today.