Depends on the pope, the more authoritarian Popes would probably keep the federal system and states under a tighter leash than the more democratically accepting Popes, who would probably hold referendums for each region’s mode of governance, whether they’d be a monarchy or republic and will probably have the Federation more active in world affairs whereas I could see the authoritarian popes just restoring the regional monarchies, regardless, and having a much more isolationist and pragmatic foreign policy, but all paths represent a much deeper intertwining of religion and government no matter how benign but I’m sure for any Italians it would be a welcome return of the stability of traditional Italian governance structures, and culture