The Germans held about 80 per cent of Stalingrad at the time the 6th army was encircled.If Hitler had allowed the forces of Army group A particulary 1st panzer army to augment the forces already commited to Mansteins Relief operation[Operation Winter storm] there is a Chance for German Success.Winter storms success would have blasted a relief Corridor through the Soviet lines,allowing the Re-Supply of the 6th army.The Soviets would probably launch a scaled down version of Operation little Saturn,while concentrating their main forces on crushing the German supply corridor.
Provided that the Germans hold the Corridor through the winter,Mansteins panzers could conceivably be in a position to turn the battle mobile,forcing apart the jaws of the Soviet encirclement and forcing the Red army back to its Start lines for Operation Uranus.Axis casualities would be enormous,but Hitler might then decide to have one last crack at Capturing Stalingrad in spring of 1943.Throwing everything against the Soviets in one last surge its possible that Stalingrads defenders buckle and the Germans take the ruined city.Considering the scale of losses I don't know what they would do next,but with Hitler in charge probably something stupid.