B-L Peace on the Eastern Front in 1942-43 - what happens to the USSR?

Let's say that the Nazis manage to extract a Brest-Litovsk-esque peace from Moscow in 1942-43 - what effects could this have on the USSR? What does the USSR look like after this? Does it become a "Union of Soviet Siberian Republics" i.e. a rump Soviet Union which still controls much of Central Asia and non-European Russia?
 
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