Reminds me of how a stray shot from a Vex hit and knocked out Sagira back in the Curse of Osiris. Her eye lens was cracked and the rest of her outer shell was still intact and held together, and even so Osiris already had some sort of machine waiting at his disciples’ station in the EDZ to kinda phase her into another ghost shell. I guess that they can still kinda come back (in one way or another) so long as their main core casing isn’t completely destroyed or breached, though whether it can be from another ghost or from a deliberate method like Osiris’ is the real question.