The majority don't quit the MMO when they max out unless the game has no content outside of leveling. The catch with MMOs is that its more about the community that you become a part of than the max level. The problem with DF is it just has no content outside of death match style combat system.
I'm not sure if "winning" DF means the same thing as it did in SB but if it does then that just goes to solidify my point about the game dying. how can people not playing the game can cost LoD a victory? I mean it's unrealistic to expect people to play games they don't like and its unfair to blame someone for "losing" when they don't even play.
LoD is part of a major alliance (zerg) in DF having 20-40 more people would hardly be relevant imo.