the most decisive battle in the second world war was at stalingrad, it led to the defeat of the german 6th army and destroyed most of the 1st panzer divsion. this was then followed by a soviet victory at leningrad and the push from the soviet union all the way back to berlin, were it was seperated between the french, british, american, and soviets, who built a wall to secure their workers from fleeing to the so called "west" section of berlin to find better jobs.
but if the germans retreated from stalingrad and held postions some where near the ukraine or deeper in soviet territory, they would have exhausted the soviet counter attack and possibly regrouped and pushed towards moscow and the caucus region