Another thing to consider, if I defeat a player with a large mineral reserve, I should be able to cart that off. If he respawns, I lose my "prize".
As it is though, changing mechanics could cause issues. One possible solution is that after a respawn, all your structures remain so long as your rooms aren't empty (like how you can't destroy a structure with hostiles in the room).
If we let controllers downgrade normally, then we'll see a large number of people abusing that and preventing others from remote mining in that room.