You could implement a rounds concept similar to CS. When you are killed then you are dead until the round ends i.e. either your team or the enemy is wiped out or objectives are met. This would allow new players to join the next round, and you could return state of all objects back the their original, game beginning status. This would prevent the mass amount of data that needs to be sent to someone joining during play. Now if you allowed a spectator mode, then you would have to send the data to the user. Just an idea.
