Add a vote for surrender. If it passes, the citadel gets destroyed, everyone gets his fav points until that time and the game ends.
I don't think it's a good idea to negate the AI and just lose one demigod from game. The AI can still be of some help (lol, in some cases he's doing a better job than the rage-quiter). On the other hand, he can die easily, because he makes some stupid mistakes sometimes (that should be corrected by GPG, btw).
BUT, there is imo another way to improve the game, making games last longer and harder to predict. The way it is now, most of the games are decided at the begining, when the first 2-3 dg kills are made. DG kills give a lot of money to the two players who make the kill, and so they will have a BIG advantage, because money is very important in this game. The other team, if they cannot kill a DG at the very begining, they have lost the match in 95% of the cases. And this is the time when most of them just quit, because it's a waste of time, they will only get killed more and more, as the opposing team has more gold to buy better items and such. The solution is simple: have the creeps give more gold to the demigod who killed them. Or when somebody captures a flag, give him some gold. Let the poorer demigods farm for money also, not only for experience. So they can still have a chance in the second part of the game. This is more important in games smaller than 3v3, imo, not so important in 4v4 or 5v5 matches.