Could a criterion for "deep enough in" be implemented after which resigning a 3-player game lets the bot finish for you, but doesn't deprive the other players of their game for rankings purposes?
I've often been annoyed by, say 10, 12, 18 turns in a player resigning from an obviously lost position and a game I would have won turning into an unrated game. I just saw the most obnoxious version of this deprive one of my opponents of a win: he'd played better than the other two of us (and had a bit of luck), and was literally in his last turn, when my other opponent resigned and turned the game unrated, depriving him of his win. I hope at very least the resigning player gets a loss so this isn't a way to game the 3-player rankings.
Some criterion like resignations after 10 turns, or after a pile is empty, or after there are fewer than 6 provinces (or colonies) remaining lets a bot finish for the resigning player, but keeps the game rated, would be most welcomed.
(It would be better to do this if the bots play ability was ramped up a little -- recently in a bot match I had Lord Rattington play a Legionary and not reveal a gold, then play a gold in the buy phase, I'm mean the bots are supposed to be artificially "intelligent"...)