Based on what the team has said, I don't believe they will attempt to implement re-emerging factions. If I understand the mechanics of the game correctly, the only way it is possible to have a faction re-emerge is to designate it as non-destroyable, which I think is applied to the Papacy in vanilla M2TW. I haven't actually played a campaign in which I (or another faction) attempted to eliminate the Papal States, but I've read that even after their last settlement is lost, they will reappear in a few years by requesting land from other Catholic factions. So I don't know if it could even be applied appropriately to a non-Papacy faction.