I've heard that Stalin offered three peace deals to the Germans - I'm not sure if it's true, but for the purposes of this thread, we'll assume it is.
The three deals offered (and ignored by the Germans in OTL) were:
1942, after the start of the German summer offensive: Brest-Litovsk borders.
1943, after the surrender at Stalingrad: 1939 borders.
1944, right before D-Day and Bagration: 1914 borders.
I also heard that the Germans seriously considered the 1943 and 1944 proposals, but decided they could stall for time and a better strategic position. After Bagration, the Soviets cut off all communications to Germany, thus dooming them.
It's theorized that Stalin may merely have been attempting to sow discord among the German army, due to their necessarily more realist view of the battlefield than Hitler (and indeed the rejection of the proposals, especially the 1943 one, added several conspirators to the July assassination plot). However, we'll assume he was genuine in offering a peace deal, but the war would begin anew when the Soviets thought they had rearmed enough.
What would be the effects of the Germans accepting each of the proposals?