Even with the concede I still see people quiting, not even sure why - in some cases they die a couple of times and leave - but the game is nowhere near over.

I can't ever see the AI being a good replacement for a good human player. When someone quits or disconnects how possible would it be to either have a way for all the players to go back to the lobby area (i.e so they don't get lost when a new game is created). This could be done through a vote which may get round the issue when one player is known to be lagging the game.

Alternatively have an area in the games listing which shows games that have started where an ai has taken over so players could join in the game and replace the AI.

Another alternative is not to replace the player with AI but give the team a bonus in xp/gold/level or similar?

Maybe their won't ever be a solution but I think the relatively small arenas one player leaving does have quite a bad affect.

Tals