Fall Blau would not have changed the course or outcome of the war in any way. The Soviets so thoroughly sabotaged the oil fields at Maykop, prior to retreating, that German engineers estimated they would need no less than 12 months to get the oil wells operating and that it might be easier to just drill new wells [which would also take about 12 months]. The Soviets were experts at sabotage/scorched earth prior to a retreat and they would have thoroughly sabotaged Grozny and Baku oil fields as well.
Soviet oil production increased even as the Soviets fell back within the Caucuses because Stalin merely ordered production in the Urals to increase with new wells.
Germany was so weak in 1942 that they were not able to advance along the entire front as they had done in 1941 with Barbarossa. In Barbarossa they advanced along the entire front with 3+ million men. In 1942 they were so weak they were barely able to sustain an offensive [that ultimately failed] that involved one army group along their southern axis. By 1943 they were so weak they were barely able to launch an offensive in one sector of the Eastern Front [at Kursk].
Germany did not have the economic strength to beat any of the major allied powers, whether the USSR, USA, or the UK, even if that power was only fighting alone.
Britain had the world's largest empire and access to resources and manpower far in excess of anything Germany could ever hope to field.
The USA had a GDP about 3x that of Germany and a manufacturing base that Germany could never hope to match, let alone beat.
The Soviet Union had a manpower reserve, mobilization ability, and small arms, tanks, etc., production ability that Germany could never hope to match.
As soon as Britain and France declared war on Germany in 1939, and Britain refused to negotiate a peace, it was inevitable that Germany would eventually lose to the British Empire.
If you read Wages of Destruction by Tooze it is clear that even Hitler knew this. He told his closest advisers and major industry chiefs that German steel production was an Achilles heel, along with the food supply, and that if Germany could not find some way to force Britain to make peace, Germany would ultimately lose. The invasion of the Soviet Union, which made sense at the time, was actually a move of desperation on the part of Hitler. It was an attempt to remove the possibility of Soviet intervention on the side of Britain, from the equation, and pressure Britain into making peace.
https://www.amazon.com/Wages-Destruc...of+destruction