Insurgency will always appear in an after war situation like this. With the support of adversary, they'll bite and can make the effort to rule the area become very expensive to Moscow. But there is another factor that can enter the calculation here. Like how far Moscow value the land compared to the cost of the insurgency that they have to fight for a very long time. If Moscow consider that the land of Ukraine that they take is the core / heart of their land and history, they'll eat all the cost that they have to pay in order to protect the integration of the East Ukraine to Russia. Sooner or later, this insurgency will be extinguished. And the attempt to retake it from Russia will be futile. But it all depend on Moscow and how they handle the people in the area. And of course, how capable are they to close the border to the west.
