I think we should encourage players to remain
active in the game up until either a) the team resigns and loses the game or b) the player resigns and leaves the team (becoming a spectator or just leaving the game altogether).
Implementing teamspec would encourage players who have lost all their stuff to stop helping the team. The best course of action - and one we should continue to encourage - is that they're given some units to control so that they can keep helping their team.
If someone wants to stop playing, they should be dropped from the team and treated like any other spectator.