Even better thought experiment: what if Hitler hadn’t attacked Russia, at all, and had instead saved that energy for attacking Great Britain.
Withdrawing from Stalingrad wouldn’t have changed much. The soldiers that died at Stalingrad would have died on the march home. The Russians would still have pounded Germany from the East and the Allies would have pounded them from the west. The timing is all that would have changed.
“what if Hitler hadn’t attacked Russia, at all, and had instead saved that energy for attacking Great Britain”
Wouldn’t matter if he couldn’t muster a ground invasion against Britain, and he couldn’t do that without defeating the British navy, which he failed to do.
Stalin was planning on launching his offensive war by 1943, had the Germans not attacked Russia before. He was trying to buy time until then.