Very good, Frogboy. I was going to recommend this myself, so I'm glad I checked to see if it has already been posted.
HOWEVER, I have some additions to this.
1. When conceading, Have it start a vote on the conceading player's team asking all players on that side if they want to Concead. If the vote passes, the game ends immediatly for all players, giving a win to the other side.
2. To prevent abuse, put a timer on when a game can be conceaded. 15-20 minutes after the game has started should be plenty of time before a team knows if they can't pull a merical out of their ass and turn their near-loss into a win.
On the other hand, if players want to continue, and one player needs to leave, and/or only him wants to concead, then as he leaves, all items he owns get sold, and all money he has gets split between the remining players on his side, as well as a portion of his exp, to make up for the lack of his support.