The Nazi government probably ceases to exist within two decades. Germany itself may remain a large power in Europe however even after.
Most of the German economy grows as a result of military spending and taking what it can from those the government eliminated or occupied. Once the fighting in Europe ends drive in the economy will decrease greatly and stagnation will set it. I would say within a decade, the wealth stolen from further populations eliminated in the Holocaust can no longer support it anymore. Not to mention most of Europe will be in ruins needing to rebuilt, largely with slave labor and a destroyed system of infrastructure that will take decades to reconstruct. Recovery after the war will be very slow.
Beyond slaves, Hitler's other means of tapping into the conquered natural resources of eastern Europe will be to force select German families to relocate there and attempt to open up industry and farming again. Germany will never subdue the British Empire, remnants of the Soviet Union, or United States who will use their own means to undermine the Reich. They will do what they can to support terrorism, the millions of partisans who are not captured or eliminated throughout Europe. Efforts to expand Germans into eastern Europe will be under constant efforts of attack and sabotage. Little is built, many die from being massacred, malnutrition, exposure, disease, even famine due to poor planning by the government and also corruption from the military officials who administer them. In parts of Germany civil disorder will emerge due to food shortages, low wages, limited opportunity, and further.
Hitler will die sometime in the 1950s, possibly be assassinated even before then. Moderates will succeed him and see forced German expansion into eastern Europe as madness and end it. The Nazi ideology fades with the poor results produced by Berlin. Hitler's successors probably do suppress the civil disorder and demonstrations against the government with violent force which can trigger a civil war. As the German Civil War consumes resources due to infighting, it allows the rump Soviet Union to reclaim former territory it once held before the war. They will fund other uprisings/insurgents to assist in this effort. Britain and the United States also attempt to give similar aid to former democratic nations in western Europe. The Soviet Union may by this time resort to a command economy with a more hostile regime in power than the Kremlin would've been.
The moderates that claim victory over Berlin agree to withdraw German forces from formerly occupied territories. Germany probably is controlled by a military junta seeking open relations with the West sometime in the 1970s. It'll probably take half a century for Europe to have any sense of recovery. A military and economic arms race of sorts does occur between the rump Russian state and western Europe. It won't be on the scale of the Cold War though.