Yeah, sure, but how exactly are they back? What are the mechanics behind it? How do they plan to become relevant to Faerun? Maybe... through heroic, almost miraculous deeds?
Probably related, but there is a lot of overlap between Illithid reproduction, Bhaalspawns in the previous games, githianky child rearing practices and different "True Souls" trying to kill each other. Illithid tadpoles eat each other in the nursery, and the ones who survive are chosen to be implanted, Bhaalspawns killed each other, Lae'Zel explains that she killed her own cousins to prove her worth, the Absolute's True Souls are pitched against the survivors of the Nautiloid... (suggesting that the Absolute's tadpoles do not particularly like the new tads on the block). In turn, their adult forms are eventually devoured by a larger, more powerful and domineering entity (an Elder Brain, Bhaal himself, Vla'kith, and whatever the Absolute is).
It **would** make sense for a god or an entity to attempt the ultimate devouring -- a god itself, AKA, you if you go that way. I guess that a way to resist this pull would be to create strong ties with your companions, much like the tiefling kids and even the goblin children stick together. Keeping in touch with the real world and real people, so to speak. IDK.
