Fandaniel and the Depths of Ascian Tempering

[Mieck]

Death = Untemper

Aren't Asicans "dead" by virtue of their very nature?

Thancred - "Crystals? You mean... like the Ascians?"
Urianger - "Just so. As the Ascians flee unto the rift 'twixt planes with Crystals of Darkness, so did these warriors come hither with Crystals of Light."
Warrior of Darkness - "Eloquent as always. Aye, like the Ascians, we too are beyond death! You cannot defeat that which is eternal."
Alphinaud - "Wait! Such methods as the Ascians employ require the renunciation of the flesh. You... you would have had to..."
Warrior of Darkness - "At long last, you see. To save our world, we gave our lives."

If death untempers them, then there is either a mechanism to re-temper (perhaps that Aetherial Rift amphitheatre with the Zodiark statue at its core?) or there is a kupo-ton of hot air that we've heard from all the Sundered. As you've already pointed out, that would be a lot for the writers to handwave away.