Best case scenario is, what if Hitler takes Moscow, and as a result, Stalin is overthrown (my guess is that Khrushchev very well may have been the one to engineer such as coup), and Russia still defeats the Nazis.
If Hitler gets Moscow war is probably over. Moscow was the hub of everything in Russia. Stalin was all about central control. It would have knocked out their central communications center. All rail lines etc. ran though Moscow. Really hard for Soviets to over come that.