If Vatican ever (God forbid! *crosses himself*) invades Serbia,
I like to think about it as too abstract, fantasy and ridiculous. BUT, considering what kind of pope it is in Rome now and history of Teutonic order and invasion of Byzantium by Catholic forces while severely threatened by Muslim invaders.
It is not something that can be written of as impossible due to history.
GROM would most likely have to be used indeed to straighten him out if such a mad decision would been made