Russia is not going to threaten the sovereignty and territorial integrity of the former territories of the Soviet Union.
No one can exclude the possibility that Ukraine will start disintegrating itself, as the regional elites no longer need Kyiv.
Poles, Hungarians, and Romanians have their eye on the Ukrainian territories, which historically were part of Poland, Hungary, and Romania. As the situation deteriorates in Ukraine, protection of national minorities will become in issue. Furthermore Nazi structures, prominent in Ukraine, may push the government to attack Donbas.