Most big company CEOs are not the biggest shareholders in their companies. If AI really does get to the point where it can do almost every single possible job more efficiently than any and all humans, then CEO jobs are no safer than anyone else's. Zero, one, a few, or in theory (but unlikely in reality) all people will make production decisions for the AI and no one else will do anything of economic value whatsoever. That doesn't mean some humans won't "work" - humans will still be able to make nice wooden tables, for example, but in such a world the AI could make better tables faster, cheaper, and with less waste of resources. For a person to sell a table that they made, they buyer would have to want it because it was made by a human - despite it being inferior in every other way.