Actually I really like the "rebels". In my Gallic (Averni) game, I see them as indendant tribes on my territory; they behave this way, sometimes staying where they are for years and decades, somehow neutral to me as long as I say towards them.
Their "ravaging" the tiles around them, in my understanding, means that I don't control the ressources in this area, which makes sense. So actually my still weak empire is filled with such semi-autonomous tribes.
Sometimes one of them gets too agressive (a political conflict explodes) and I have to defeat them. And one day an ambitious King may just defeat all of them and impose its rule all over the "Averni" territory...