This scenario is a delicious nut to crack.
I managed to do it in seven turns yesterday, and today I did it in six. Without using prestige!
On Soviet troops not trying to recapture the supply points. I find that to be somewhat realistic.
We have to keep in mind that the idea itself of the Germans disrupting the soviet logistics in this way is a bit unhistorical. But... If they first managed to do this, captururing supply depots so far from Stalingrad itself. There is no land beyond the Volga! At this point the Russians where pouring everything(More or less) into retaining Stalingrad. Any repositions would probably serve as an unforgivable change of priorities. I would think Stalin waited to after this victory for before finally understanding that he should let the generals who actually knows how to fight the war, be in charge of the war. Where as Stalin grew to trust his generals with decisions, Hitler blamed every failure those generals in charge and resorted to disastrous micromanagement.
On a side note, the hoarder and the completionist in me is tortured by the thought of spending prestige. If it can be done without help, well, then it has to be done without help.