This is a horrible idea because honestly a team wouldn't let the other quit. If I spent 10 minutes in a game and two of your players rage-quit, I wouldn't say, "Meh, no biggie, 10 minutes wasted, but for YOU I will drop the win ." Players might use the option once or twice, but once they see it happen over and over, they are going to be JUST as tired of leavers on the opposite team as they are currently with them on their own team. It would just cause even more games to be disrupted.
Plus, this would have to be agreed upon by 5/5 on the opposing team, otherwise players would just be extremely upset that their team-mates cost them a win.