As far as I know, the Papal reemergance is similar to any other faction reemergance, with one caveat. Usually, a province has to have loyalty issues to allow for a faction reemergance. I don't think the Papacy requires that, they can spring up in provinces with pretty solid loyalty. He does seem to favor provinces with fewer troops (smart cookie, that Pope), so pick one province you don't really want and pull out your troops. Let it rebel and let the bandits have it, and in 2 or 3 years, you'll be crusading happily again.