Thinking of this passage from episode 197 with regards to Simon Fairchild:
BASIRA: What happens to you if they escape? What happens to us? We’ve all been touched by them.
ANNABELLE: I would either travel with them, or I would die. I do not know which. My life is only sustained by The Web. Most would simply lose whatever power they have been gifted.
Jo n would lose much of himself, the parts of him that are The Eye. But he would survive. And perhaps more importantly, he would remain who he believes himself to be.
I think it's interesting Simon Fairchild not only remained in the original world but also remained pretty much intact (until he wasn't lol). As old as he was, you'd think he'd be completely sustained by the Vast and fully reliant on it to live.
It really showed how strong perception was to outcome when it came to the Entities. I think Simon perceived himself so much as himself and as free from it all as one could be that when the time came, his ability to divorce his definition of himself from being reliant on the Vast was very easy and very simple. Simon was himself through and through the whole time, the charming parts and the extremely sadistic parts. He thought of himself and his choices as fully part of his human personality and therefor fully retained his humanity after the Fears left.
He was human because he thought of himself as such.
Now what does that mean for Jon and how much he thought of himself as monstrous and part of the Eye I wonder... And I truly don't believe Anabelle really knew what she was talking about, especially given that not only Jon vanished but Martin as well. The perception of reliance is what apparently makes the difference, not actual reliance itself