There is no simple answer to this because we do not know what the Germans do after they take Stalingrad. They would likely turn south and run out of steam. Their flanks would be stronger, but more likely than not the Russians still cut them off and drive to Rostov, trapping even more Germans.
Germany's best chance is to give up on the southern drive because they simply did not have the fuel to cross that distance and support it if they were to run into any resistance. The moment they realize its unwinnable they dig in where they are, keep the majority of their forces as reserves to react to counter offensives.
JUst like Rhzev, it is possible that the Germans might be able to fight RUssian counter-offensives to a standstill. However, as Obsessed Nuker pointed out, the USSR had 2.5 million men to bring to bear in this theater while the Germans in this scenerio would have 1.4 million.
Most likely best case "non-insane" Hitler scenerio is a fighting retreat back to Rostov. If the Germans are lucky, the Russians lost way too many men driving the Germans back. The ROmanians, Hungarians and Italians are spared destruction and are still "in it to win it" for 43 unlike OTL where they withdrew a lot of forces and lost the desire to fight.
Further, the Kursk battle of ATL will likely be around Rostov or Kharkov. The Germans will likely be on defense and RUssians on offense. The Russians still probably win. I heard plausible scenerios where a mobile defense in 43 would work, which is possible given no Stalingrad disaster ATL.
However, the US invades Italy. Italy still leaves war. The Germans lose in Aug 1945 when Berlin is nuked and the RHine is crossed. Perhaps Poland and Yugoslavia are in the western camp post war. Hungary and Romania are probably occupied by the stunted Russians.