No idea if there is a mission out there like this (if there is, point me to it and let me know which servers use it), but what about a POW type game?
Suppose your map has 2 teams, each with a base camp and a fenced off section for POWs. When a player is killed, he respawns into the other teams POW pen without a weapon. The game ends after a time limit or when the entire other team is captured.
Not quite sure how POWs could be freed, but I would guess you would need to get into an area and a gate would open. I'm no Map Editing wizard, so I don't even know if this is possible. You would also need to prevent the enemy team from killing the helpless POWs.
~ CanadianGamer