I try to avoid it unless I have the troops to take out the Pope in two or so turns. Then I keep a minimal garrison and when he reappears, I destroy all the buildings and leave (that'll show him! :) ). Speaking of the Pope, in a prior discussion, it was mentioned that the papal States rarely do well. I recently had a game where the Pope had all of Italy, nearly all of western Europe, all of the Iberian peninsula, all of North Africa except Egypt, and much of the Balkans. Alas for the poor pope (and the Mongols), they don't get glorious achievement points so I still kind of won.