They would both collapse. The Russians didn't have the economy or social structure to allow communism along the lines of Marx, while Germany has always been made up of over a dozen, at the very least, groups and states yelling at each other. What would unify them? A desire to spread west and south to regain all the lands of the former HRE? Well, besides for the Kingdom of Four Sicilies. I imagine the Germans would like Rome at their southern border as a sign of nostalgia. Though their would need to be a lot more cardinals from Germany.