I want to drop my two cents here. I see some assumptions that Orpheus is one of the good guys. Remember that his mother Gith wanted to conquer the realms herself. Doesn’t matter her motivation. Because of the split with the followers of Zethimon and the fact Vlakath stopped her this wasn’t attempted.
As such, I do *assume* that Orpheus has similar motivations to follow his mother’s footsteps. After they defeat Vlakath, they will likely turn on their Githzerai allies. And then begins their true war.
Siding with the emperor and letting him eat Orpheus may give him the knowledge to someday begin his own grand design (obviously if you allow him to become the absolute).
The only “good” endings I see with meta knowledge is Gale nuking himself, without anyone gaining Orpheus knowledge (letting Orpheus live is still a safer bet as war among equals is much better than a unified mindflayer race). Even you or Karlach being mindflayers with that knowledge is dangerously edging the grand design.
The D&D universe still has an ace up the sleeve if the grand design were to begin. That ace is the God born Dead, Atropus. He has a thing for killing mindflayers it seems.
https://forgottenrealms.fandom.com/wiki/Atropus
