If that is the case then Putin better get this war over with quickly by hitting the Ukrain with the big hammer, smashing thier military and taking control of the region.
Before installing the sepertist as the new government and getting out.
Let the seperiotist handle all the domestic messyness for a few years, while Putin and Russia claim to take their hands off the sittuation.
(Thus leaving the west do do what it won’t do commit troops to restore pro-westerns to power)
In a few years after the sepertist have taken control of crimina and the Ukraine is still struggling wiht itself. Russia can move in to do the formal annexation of the Nation of Crimina. Easy and clean.
Your scenario is unlikely. The separatists, on their own, even given monetary and arms support from Moscow, cannot possibly hold more than 1/10th the country on an extended basis. Kiev will recuperate, and given the hatreds Putin has now insured, Putin will be “in” until the dripping blood forces him out for good. Afghanistan x10, but with some different twists...