Has anyone considered Patton's War Plan to invade Russia after the War and how did it go?
There is an event after Germany is defeated called WW3? It happens for both SU and US and you either go to war, or don't go to war.
The viability of war depends on how many troops you have and how the borders of Europe look. Just watch out though, after WW2 has ended there isn't anything to do so you may as well go to war with SU (assuming you are US).