If we’re going with the assumption the crystal they found all those years ago was a sarcophagus, that might simply be a memory of the dark passenger’s “death.” If that’s the case, it might not be the sort of thing that even can be killed. Exorcism might be the better word, but if it’s an entity entirely foreign to the Fountain that raises the question of who would know how to go about it.
I mean they’d have to be pretty potent to pull that off, right?