Why didn't Durkon Plane Shift to Celestia to talk to Roy?

[Peelee]

I doubt VERY MUCH that "maybe Roy wasn't actually Lawful Good!" ever crossed Durkon's mind, for a second.

That wouldn't necessarily need to have crossed his mind. 9 alignments fit into 17 planes, it's not completely out of the realm of possibility that Durkon wouldn't know if Roy had instead gone to Byoptia or Arcadia while still being Lawful Good.