Separatist movements anywhere are bad news for everyone everywhere.
Our borders suck. Many of them were drawn as colonial or Cold War gambits with no attention to how they’d work in real life. Furthermore, countries change and develop new fracture points and allegiances all the time.
But the only thing worse than the current borders are changed borders. Nothing has caused more bloodshed, and nothing will ever make 100% of people 100% happy with all the world’a borders-- especially when natural resources are unevenly distributed. Changing borders up is just asking for trouble.
Which is why, whenever possible, countries are encouraged to work out their internal differences internally, and to think as a nation rather than as a bunch of potentially autonomous entities. Experience shows that it can be done, but not until everyone gets it in to their head that they are in it together.
Now and then there is a situation so compelling that a country goes through the long and carefully considered process of legally separating. The go through the right channels, make sure the impact on neighbors and citizens is fully considered, and plan something that is satisfactory to everyone.
That doesn’t usual involve Russia rolling in with tanks.