If the Germans would try to get out of the pocket the Soviets would know it immediately because the surrounding ring would be broken. That would release these troops to hunt the escaping Germans within hours because I do believe the Soviets were expecting that kind of reaction, wouldn´t you?

The Germans would be forced to refuel in the middle of nowhere if the idea was to attack from both sides and meet in the middle. I mean the 6th Army only had fuel to make a run for 50-60 kilometers and without refueling immediately when meeting the 4th Panzer they could not get anywhere. The distance to safety was some 100 kilometes altogether at the time I think. Hitler himself was told of the fuel situation in early-mid December and he said they would not get from Stalingrad more than half-way to "freedom". So another reason why Hitler would not let them escape from Stalingrad because it was doomed in Hitler´s eyes even to try.

"It would take 1-2 days for the Russians to realize what happened??" I do think you are quite underestimating the enemy here....

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