Here's a reason for Bryan to flee Narnia:
Bryan probably has the trust, and the ear, of the King of Archenland--or at least, of someone who outranks Steward Arlis. Arlis is the NPC in the "Anvard" thread who is trying to prevent the King from hearing about the true situation in Narnia. I think that Inkling, who invented Arlis, means him to be an actual intentional traitor, like Wormtongue. I would love to see Bryan cut that villain's head off!