Seems like they're preparing a new part of Time Temple.

The thing I'm looking for is that the Black Mage obtained immortality, and that's why the 5 heroes sealed him, rather than kill him. As of now I have no way to confirm this but to remake all quests with another character, which would take me a few hours.

I'm just digging through .xml extractions of a couple of the .wz files, so my searching methods are far from efficient, but I see no mention of the Black Mage being immortal.

I do seem to remember him being mentioned in Magatia though. I just can't remember where.
I wonder if my Pali has done those quests...