A German long term victory was technically possible in real time history, but not one lead and ruled by the NSDAP of Hitler and co. All depended on wether or not Hitler and his National Socialists were removed from the political and miltary scene, possibly replaced as early as 1938 by a military dictarorship, lead by the old aristocratic Wehrmacht high ranking officers, schooled by the old Imperial German/Pruisian Academy.
The National Socialist leadership was quite incompotent in economic affairs and supported internal competition between party officials and other top figures, rather than having a sollid economic plan to do something about the economy itself. Too much attention was focused on short term things, such as the huge unemployement in the beginning and mass armament production in the late 30's. No real long term economic decissions were taken, such as to reform the industry to produce other more complicated endproducts, rather than only crude products, mainly needed by the military only. Internal public consumption had to be increased, or all would come to nothing in the end.
Unter a leadership of a more educated military leader, Germany could have altered its destiny, by not starting WW2 with the invasion of Polland, but by seeking alternative ways to reclaim its former eastern land, first negotiating out hostilities in the West, mainly against France and the UK. Technicaly it was possible, if the Germans could be kept patient and possibly provocing Soviet Agression first, such as against Finland. With a possible back up by the Western Allies, a non-National Socialist government could possibly get more territorial claims later, even if a more prepared USSR would be faced. Soviet military leadership had been eliminated before by Stalin, so the Red Army was quite unprepared for years and not commanded by able or experienced commanders, since no real grandscale war had been given to them to gain experience.