Who will buy the bosses' shit if everyone is unemployed and can't afford it? Companies can't stay afloat by just buying from each other.
After an initial injection of capital, yes they can.
And that matters to who, and why, exactly?
Once enough of the economy is automated, there's hardly a reason for it to keep humans in the loop. It can just run in a circle, serving itself. Humans, meanwhile, will just have to barter for scraps amongst themselves.