Gale as a nuclear bomb seems to me to be the best solution so far. Mystra will revive him somehow. She has some practice at it herself.
Jenevelle (Is she actually called by her real name again if she chooses Selûne instead of Shar?) Well, anyway, I could well imagine in a sequel that a twin sister suddenly appears and of course Jenevelle will represent Selûne and Shadowheart Shar and continue the battle of the twin goddesses as mortals, so to speak.
Ascended Astarion I would have liked to have seen as another solution, and pretty much the reverse: i.e. not twisted, insane and dumbed down version of a
Vampiric Illithid or vice versa.Ascended Astarion will never agree to that. He can't be forced - he can just walk away, turning to mist. If the group destroys the Brain without his input, he's just as well getting rid of the tadpole, if the group dies or Tav becomes Absolute, he risks... becoming an Illithid? There is no leverage or manipulation to force the Ascended Astarion to become illithid. That would be a violation of his character. But for Astarion Origin, where the player defines the character's personality, and may want to become an Illithid, the option of him being a Vampiric Illithid would be a nice detail that would show a scrupulous regard for DnD lore, in this case, yes.
But, please, don't have Astarion-illithid in the sequel. I will hate this sequel if the developers do that. But, this is no longer an Larian question, Hasbro has all the rights to the characters, and we're unlikely to see any of the old acquaintances in the next Larian game.
I support the ideas with Gale and Jenevelle/Shadowheart, very interesting solution. Also Shadowheart has a strong and in a special way beautiful “evil ending” in her Origin. This new deity she's become could be a worthy character for a sequel, too.