I've been thinking about that.. could do either.. no neither
At this stage, I was sort of thinking about just leaving them be and ruling their provinces to be unavailable.
Getting a sub or setting AI could both impact the game balance pretty severely. Right now I think the game is pretty even. A human or AI deciding to go after someone would essentially take that player out.
After this many turns, I would sort of hate to see the game decided that way. I'm open to other thoughts tho of course.