There are 2 possible outcomes:
One.- Germany beats the soviets, and after a period of peace of about 3 or 4 years, germany strikes again and eats the soviets really slowly. You annex the germans there and then and the soviets are left with no gains save for their national territories.
Two.- When germany is on their death throes, the soviets will DOW germany. They will grab a few provinces, then you will annex germany. you keep the annex, they keep what they recaptured.
In both cases, the soviets are left as a pitiful force.