That would be great
As for l4d2 it would have to be on a timer, so checks lets say 60 seconds after first player connect, and do one check and only check when a player joins an empty server. Not on every player connection. So even if member leaves server half way through the match, the game can still go on, and new players (non member) can connect to the server, and the member check will be done again once server gets empty and a player will connect to an empty server. Not sure if that make sense, but i think this method could apply to other games as well.