HELP: A player wants to cast Banishment on an NPC that's not from the material plane, but dimensional travel is not possible

As the title said, but for more context, in this setting I created, a powerful magic explosion severed the Ley Line links from this plane to the other planes, making it impossible to travel to other planes of existence, but it never came to my mind what would happen if a player cast Banishment on an NPC that's not from this plane (let's this NPC is from The Feywilds). What could be an interesting result from this action? Is "they simply don't travel to the other plane" a valid solution?