That would be the 'humane' thing to do, but I suspect the AI solution would only need to keep a few people alive for maintenance until it figures out hands for wire terminals and crimper tools (dexterity). Keeping people around by the billions is problematic from a feeding, entertainment and waste management standpoint. Nothing good would come of it. The only reason we put up with CAFOs now is because the regulators like tailgate parties. AIs have no appetites to turn their eyes away from the environmental damage of cities. We think in terms of reproduction and prolific dominance to 'own the planet' through competition/war with other humans, but a robot overlord doesn't need any minions to pray and pay. A single robot can be its own legacy and longevity.

We are the all-consuming berserkers that our books and movies warned us about.