As the tin says, the challenge is to maintain the Soviet Union to the present day. However, I am going to put forward some bits to make things more interesting.
-Firstly, it need not continue in the state it was specifically. A more looser Federation, something akin to the European Union, is perfectly acceptable.
-It must be Left Wing, but it doesn't have to be Hardline Communist or Socialist.
-Keeping members of the Warsaw pact within its sphere of influence is completely optional.
-Consider this one a bonus challenge, have the Soviets be more reconciliatory (or at least not as confrontational) towards the West.
-Firstly, it need not continue in the state it was specifically. A more looser Federation, something akin to the European Union, is perfectly acceptable.
-It must be Left Wing, but it doesn't have to be Hardline Communist or Socialist.
-Keeping members of the Warsaw pact within its sphere of influence is completely optional.
-Consider this one a bonus challenge, have the Soviets be more reconciliatory (or at least not as confrontational) towards the West.