I think it depends, the Drifters experienced dying of starvation and was resed still hungry. That could be the case because their light and ghosts light were being messed with. A ghost without with light can't revive a guardian, another ghost is part of it too i.e. darkness zones. A weakened ghost may have problems reviving, either not enough light and/or can't channel it properly. Falling from the tower is a great example for this as well, during the Warlord era ghost were often targeted. I'd say under extreme circumstances you'll still be exhausted.