Depends on how much they dumb it down and take shortcuts. I think they could cut a lot of corners instead of being real AI constantly. Games where NPCs harvest resources and stuff have existed forever, just using simple pathfinding and stuff. All they'd need to do to make it feel alive is have a lot of different structures and whatnot the AI could progress towards building, and have them choose which one they're gonna build at world generation. Possibly have AI calculate variations and additions. If it's out of sight of the player it doesn't need to be true AI or even real-time.