Honestly, a game needs good players as much as it needs a good GM.  Attrition is going to happen, but when playing a group game people very much need to have a team mentality.  Unfortunately if not everyone is doing all they can to make the game enjoyable for everyone then the game is more likely to fail no matter how awesome the characters are or how well the players can write and no matter how much effort and creative genius the GM puts into it.