I think the whole thing depends on how much u want to cry about finishing a game.
In Custom, if someone drops, why bother sitting around to get beaten by a team with more players? If you can beat such a team, you were always going to win or u had already won. Just finish and start a new game. It's not like u lose points or ranking or anything. Of course, u might want to test yourself to see if u can beat unblanced teams. Whatever. U don't need AI.
In Pantheon, if your team mate drops, think whether you can beat your opponents even tho u are man down. If the answer is YES, good luck, get some points. If no, quit. Start a new game.
It's Pantheon, man up and stop whining about wanting an AI 'helper'.
The trouble with AI is that u don't want something artifical dictating the outcome of a MP game, whether it be because they give too much gold/xp OR cos they make the AI too useful (ie make him rock hard).
BUT, in Custom, it doesn't really matter what u have I suppose. Hell, for all I care, put in an option that lets you replace a human with a nuclear powered grenade launching assassin... oh wait, that's Regulus... hur hur...
Pantheon must NEVER have ANY AIs in it.
Random teams, equal number of players, no AI. First to 1 mill.