Well, been thinking about how to retire Mystic but it's rather hard as there's not any particularly good way to retire her that's In Character for her, and there's no way I can retire her in an in-character way and ever bring her back.
So, I'm putting Mystic as Permanently retired. She probably helped out Sandy to make amends as best she could before whatever it is she ends up doing. At the moment, the only In character end I have in mind for her doesn't work too well, as it implies completely abandoning Faithful Song.
I'll talk it over with Lix when she wakes up tomorrow. If there's some way Mystic could make sure Faithful song was in good hooves before she left, she probably would.
I'll report my findings and the ending for Mystic as soon as I can.