They must love their man! Did you ever find out what happened to him? Was it a brush with a predator? The girls remember that sort of chivalrous behavior.
If I were in your situation, I would opt for euthanasia.
This type of damage is not typically something they come around from without surgery to repair the inner damage.
In my experience, small animals can astonish you by their will to live if you give them just a little bit of affection. Some people may disagree with me, but I feel he appreciates and understands your doting on him.