Well presently Russia turns into IMPASSABLE after the revolution so just making it neutral is a small step toward reality. The CP can keep going to Moscow if it wants, but that reactivaes Russia as an allied power, conversely, if Russia is almost empty the allies can invade to get to Moscow and turn back the revolution (by fighting their way to the Kremlin)
Otherwise, both van ignore Russia as it sorts out its own internal affairs.
I would go as far as having a die cart you roll each turn to see if/how the revolution ends. Some result rejoining the Allies, some remaining neutral, some trading with the CP, and an option to Join the CPs.
Would probably be 2d6. 6,7, and 8 being “stays neutral roll again next turn”