On the other hand, having a few Ascians left alive would allow for more Gaia-esque situations. I could see one or two being disillusioned by the way things have gone and choosing to throw their lot in with us instead of Fandaniel and/or Zodiark.

That said, three trials and a solo duty would probably be enough to completely deal with the remaining Ascians aside from Fandaniel. I'd say that would be a bit monotonous, but I'm fairly confident they can make things interesting if they go that route.