Something that struck me after a recent re-read of WLW: it doesn't make a lot of sense for Yatwer to work against the Great Ordeal through Sorweel. If anything, it seemed like she wants to prevent No-God from returning. These two lines from her POV seem to refer to the stillborn epidemic during the FA:
So many. So many children born...
So many taken.
The whole point (ostensibly) for the Great Ordeal is to stop the World being shut from the Outside and the cycle of birth ending.
I seem to remember a professorplum on Three-Seas? Cheers, regardless.
I agree with Wielokropek:
There's nothing in that passage that seems to prime us for thinking about the apocalypse; nevertheless, you could be right about them referencing Yatwer's motivations.
However, I do think that the perspectives of the Gods and the White-Luck get the lucky advantage of ultimate non-sequiturs because they seem to be able to reference the narrative entire from the objective standpoint of what will happen, even if they fill in gaps because they don't have all the details.
I also think that you may have rejected some considerations. But to the points at hand.
1. Khellus' motivation is something other than what he's stated. Which wouldn't exactly be shocking becuase, well, he's that kind of dude. But it's one of the only pieces of evidence I can find in the books that actually points to his having an ulterior motive.
So you reject the narrative implications that the Gods are blind to the actual being of the No-God? Because that seems to easily frame the tension between the Gods stringing up Kellhus' noose and waiting (erroneously, probably) to see what Kellhus plans on doing...
2. Sorweel is wrong about Yatwer's motivation. RSB clearly has a fondness for unreliable narrators (Akka in PON) and it wouldn't be a shock if Yatwer is after something less straightforward than killing the Aspect-Emperor. It could be as simple as his being a "sleeper" as has been stated in other threads: Khellus successfully prevents the No-God from returning and then Yatwer gives Sorweel the go-ahead to salt Khellus.
Sorweel is constantly coming to greater realizations - we can't very well deny the validity of a coming of age tale where revelations actually change the character's perspective and offer wider focus. So he is bound to be unreliable, it doesn't necessarily add or detract to your argument, if we reject only Sorweel's perspective.
The question you've asked, I think, really suggests that the God of Birth should notice that all babies are stillborn. And that itself asks whether the souls that are denied mortal frames are sucked into the No-God Soul-Vacuum, whether they go back to the New Soul Repository, or whether they shuffle along to Oblivion or Redemption (as sinless innocents)?