CEOs absolutely cannot be replaced by AI because the role that CEOs are meant to fulfill is accountability. When things go wrong, they get passed up the chain, and the CEO is at the top of that chain. Though, it's not like human CEOs are held accountable either, just that in theory, they're meant to be, and AIs would be impossible to hold accountable. Currently, CEOs get the best of all worlds - they get huge bonuses when the company does well, and they are sheltered and fall upwards if the company does poorly