A few threads as of late have established the following as a likely course of events--
-Case Blue is never taken over by Hitler, the original plan was to take Stalingrad before the mad dash to the Caucasus.
-Splitting AGS to AG A and B created massive logistical difficulties when AG A pivoted south. A sane Hitler might* have avoided this and let the plan go as is.
-To quote WIKI:
The success of the initial advance was such that Hitler ordered the Fourth Panzer Army south to assist the First Panzer Army to cross the lower Don river.[34] This assistance was not needed and Kleist later complained that Fourth Panzer Army clogged the roads and that if they had carried on toward Stalingrad, they could have taken it in July. When it turned north again two weeks later, the Soviets had gathered enough forces together at Stalingrad to check its advance
-If plan goes as is, Stalingrad likely falls on the march.
-The Germans probably shore up their entire line on the Don river (something they never completely done) and then sprint south, their advance ending roughly where it did IOTL.
-The Don river is highly defensible, as its shores are cliffs. Without use of the Volga for transportation, the Russians would not be able to supply a northern pincer for Operation Uranus. Any counterattack would be in the south, how far south depends upon how far south on the Volga the Germans get.
-It is worth noting that the Russian supply situation without the Volga and Stalingrad gets tenuous, as I think that all supplies would have to be carried through the Caspian sea.
-Because of the above, Operation Uranus fails, which means the Germans are on the Volga until summer 1943.
-Russia had only a year's reserves of oil. Without the Volga, Russia essentially will get cut off from almost half of all their oil (some will still make it north through the Caspian Sea. Possible ATL German bombing missions may disturb production in Baku. Something they may opt to do when they realize they cannot stop the Russians from sabotaging the wells after capturing Maikop.)
-So, by mid 1943, the Russians have to win a Kursk-like battle...or they run out of oil. The problem is the Germans never lost sixth army or all of those men in Stalingrad. The Germans would be defending on the banks of the Don. The Russians would also be low on fuel, and confidence after winter setbacks (other than operations in the Leningrad theater, probably.)
-If the Russians fail to retake Stalingrad in mid 43, the war is pretty much over for them. They will sit back and wait for the western Allies.
Now the above can still lead to German failure (Wallies clobber them, they withdraw significant amounts of men to shore up Italy, etcetera.) and it ignores other possible hindsight decisions (sending Manstein to Leningrad early instead of to Sevestapol in 42). However, if the Italians are never crushed in Russia in 42, their desire to fight is upped a bit, the Germans situation in the Mediterranean mid 43 not quite as disastrous, which means Russia may drop out of the war, as without fuel they cannot keep fighting. PLUS, Russia had famine in 43 which was alleviated by recapturing huge parts of Ukraine...here that does not happen. Plus, they do not get the manpower bonuses of recapturing significant amounts of their territory back, so in fact the Waffen SS and force labor conscriptions gets these bonuses. Its enough to force Russia out. Even if Germany can only take out 1,000,000 men from the Eastern front (the rest will have to occupy and screen the Soviets), the Wallies
never dealt with an army group equivalent of battle-hardened veterans from the East. The Germans may successfully knock the Wallies out of Italy (which
almost happened in September 1943) and this forces the issue of Overlord 44, which might fail or become a friggin quagmire the Wallies won't have the stomach for if the Germans agree to some sort of peace that let's France off--if they don't entirely knock the Allies back into the sea, which isn't entirely out of the question.