Unfortunately it's been a very long time since I've seen any successful revolts (in fact right now I can't remember any) but I would be nearly certain only the cored provinces secede. If you release a country from the politics tab it receives only the provinces on which it has cores. .
Succesful non-nationalist rebels are, surprisingly, not that rare. There are a LOT of smaller nations sporting funky flags as the result of anarcho-liberal, communist, etc rebellions in my game.
Also I watched Ethiopia secede from Egypt... not a big accomplishment since the British still held the center of Ethopia, but hey, it's another conquest wargoal for me.
Last edited: