I could be mistaken, but...
One alternate history scenario I've seen suggested over the years is for AGC to have gone directly for Moscow rather than turning south to assist AGS in Ukraine. A common counter to that is that it would have left AGC with a large gap on its flank that the Soviets could have exploited, to potentially knock out large portions of AGS, and thus it wouldn't have been a useful strategy for the Germans to try, or some sort of silver bullet to get the Nazis to win in the east. But then, Hitler didn't always make the best strategic choices...
So maybe that could be a way to get the "AGS encircled and destroyed near Moscow in 1941" part without needing to resort to ASB, perhaps in this alternate scenario Hitler gets overconfident and perhaps ignores the warnings from advisors and generals, or something like that
I'd definitely concur that "going south in 1942" to Stalingrad and the Caucasus would be unrealistic, though, with that scenario, and that they'd instead be focusing on trying to stitch together a new frontline in the center
Maybe instead of cutting off the German forces in the Caucasus, you could get a second sizable encirclement of German forces by the Soviets in 1942 a different way. After the 1941 encirclement of AGS, perhaps this leaves the Germans with an even bigger hole in their front that a Soviet offensive could then exploit for further advantage. Though perhaps at that point, logistics could limit the ability for the Soviets to make sweeping gains of ground that could allow for such additional major encirclements on that sort of scale. Though the Soviets would still be in a much better position having gotten a decisive win against AGC