We know the artifact from Shadowheart prevents ceremorphosis from advancing and completing
Do we?
As far as i know, even if Shadowheart is not in our party and she still have the Artefact (meaning we dont), nothing is happening.
I mean, as far as i know, all the Artefact do, is blocking out the Absolute. O_o
Where did you get this?
at some point I imagine that we will have to make a choice between getting rid of the tadpole or undergoing ceremorphosis but what then?
Since we have seen our party runing around City of Baldur's Gate ... and we were told by Larian themselves that city is final part of the game ...
I imagine that if such situation indeed come, it will be Game Over no matter wich option we pick.
To the best of my knowledge there has never actually been an Adversary in D&D
Isnt Omeluum one?
Illithid with his own mind, capable of resisting the Elder Brain?
ceremorphosis completes(assuming that's something the game allows to happen)
I for what is it worth, dont believe even for a second, that game would allow that to happen.
Especialy not us continue any play as Illithid.
As far as i know, it was confirmed (or spoiled, depends on point of view) by Swen himself back in early days of development, that Mind Flayers are NOT true antagonists of this game, more like just a tool in hands of true BBEG.

So i think any conspiracies that go futher than that are false.

Sory.