Non restrictive relative pronoun

The protagonist is one of Amber's royal family members, who can communicate one another through cards with their portrait on it.
The protagonist of former series of this chronicles is missing after the former, who is the farther of the latter's protagonist.

I wonder where he was?if he were even among the living. No one could reach him via Trump, though that didn't necessarily prove anything.
..............
One rumor had it that~.
Another was that he had entered the universe of his own creation and never returned, which is seemed possible could remove him from the reach of the Trumps.
["Trump of Doom" of The Great Book of Amber by Roger Zelazny]
I'd like to know if "which" is the subject of "could remove."
Thank you in advance for your help.