The reverse would also be nice. When someone quits or disconnects from your team, either replace them with a stronger AI or give the whole team an in-game buff to various stats to give them a better chance of actually having some fun.

In fact, I'd rather have the buff than a concede option. What's more fun? Agreeing that the game sucks, exiting and trying to start a new one? Or having your team boosted, or having the missing player's AI controlled demigod boosted to a point that it's actually useful. The second option at least lets you still have fun playing a game.

I'd much rather stay in a game, knowing that losing a player wouldn't mean I'm going to lose the game automatically, than conceding and having to wait for a new game to be created and connected to.