I would expect it would be the military that will coup the civilian government once they realize that the war is lost. Most of the ideologically aligned and motivated people are dead at this point. So, the morale within the military is pretty low, and the understanding that they're just being used as cannon fodder for NATO is sinking in. I don't think there's any chance of communists getting in power there. What's most likely is that Russia will install a puppet regime as part of the terms of surrender.