Just a side note from another cooperative game's perspective. I play Pandemic mostly solo and sometimes I realize the game is already lost. For example, after realizing too late I discarted too many cards of one color before finding its cure. Under these circumstances I've conceded more than one game.
My point here is that forbidding conceding for all coop games as some players have suggested here because of their experience with Hanabi would not be the best approach for all coop games. In my opinion players should be able to collectively concede a game, all taking the elo penalty (or whatever). as a team The interface would be similar to abandoning a game, with all players agreeing to concede.