Sundering stuff established in the Q&A

[Lurina]

That is the question we have to answer and why I’m curious about it. It’s possible she wanted him to remain Unsundered so as to retain some ability to remember Elpis, perhaps with the goal of having him remember, explaining her plan, and then having his aid.

Just theories though at the moment.

The quote from the Q&A begins by referencing the scene in Ultima Thule where Emet discusses the idea that his role in what has happened has all been a part of Venat's plan, and then expands from a place of confirming the accuracy of his supposition. "As you think back to the text towards the end Emet-Selch did imply that Venat let him live unsundered. In fact Venat did intentionally leave a tiny floor in her Sundering attack... (etc)"

As a reminder, this is the quote from Emet which is being referred to here.

So here I am, Venat. I suppose you needed me to tie it all together, these frayed threads of history.

In my opinion, in context, this represents a implicit confirmation of what Emet is saying in this scene - that she spared him to "tie these frayed threads of history", which is to say, to resolve the time loop.