I restarted the mission and it ended as per normal. No idea why, I guess it was a bug stopping me from finishing on the first playthrough.
None of the Soviet missions are particularly hard bar 7, even on hard mode. Good micromanagment of your forces on 7 so you can get all the money crates, capture a building in the south-east base and slap down the barracks to capture the whole lot is all you have to do really. 2-3 battle bunkers and a telsa coil (and more if necessary) at each chokepoint, capture the war factory + service depot to replace the MCV you'll probably lose to starflares at the top, and make sure you have aa defenses protecting the south-east plateau nuclear reactor. The crates disappearing bug is a real bitch, because you have to do this all in one playthrough and should a terror drone infect the Centurion you're in trouble.
I suggest capturing the reactor with a emperor tank until your defenses are strong enough to stop starflares completely and keeping an enemy tesla reactor in the base as well (4 flak cannons at the nuclear reactor, four just below the war factory, four below the service depot). That way, if the starflares are going to destroy the tesla reactor you can just capture the reactor = instantly saving your Nuclear Reactor as the starflares stop firing.
My problem is now that I've 'won' mission 8 (well, I've destroyed all of yuri's forces and the mental omega after he rushed me), but the mission doesn't end + my objectives don't change after I destroy the omega device itself.