Hi! So I have a crazy theory regarding the Neverseen and Greyfell. But first, it will require background info.
My theory begins with me rereading KOTLC for the 10th time. I'm reading Lodestar, and I notice something. When Tam, Fitz, and Sophie are at the Neverseen's hideout that's connected to the silver tower, they are confronted by the Neverseen. They knock out all of the members except Keefe, who takes Tam, Fitz, and Sophie's leaping crystal to Alluvetere with him, back to the Neverseen. So then Sophie calls Silveny and Greyfell to help pick them up. When Greyfell arrives, he looks uneasy. I seriously doubt he would look uneasy for some random reason. So this is where my theory comes in.
I think that Greyfell was attacked by the Neverseen. Remember when he was first introduced, and Sophie reads his mind, and apparently he was tortured. No one knows how long the Neverseen was around, so I think that he was attacked by them because they knew how vital he was to the timeline of extinction.