No one really knows for sure about that, especially once the U.S. entered the war after Pearl Harbor. The battle of Stalingrad ended in February of '43, so it's anybody's guess what would have happened. That division he sent to Greece may have been decimated by the Russians just as easily. And even if he had managed to take parts of Russia, he would have never been able to conquer the whole territory quickly. There were no guarantees for Hitler when it came to Russia.
But it seems likely to me that an extra division would have changed Stalingrad from a loss to a win.
The Russians would have destroyed the oil fields before the Germans could have taken them. Even of the Germans got the oil fields producing, how were they going to transport it of refine it? They had no tankers or a surface fleet to protect them even if they did. Hitler should have used the forces he sent to capture the caucus’ to secure the Volga and drive to Moscow. In the end it probably didn't matter because eventually the Russians would have overwhelmed them.