So in Dominion we have a situation where, by 1952, the Eastern Front has stalemated on a front that roughly corresponds with the Arkhangelsk–Astrakhan line that was the original stated aim of Operation Barbarossa. As you say there's an endless guerilla war behind the lines and no prospect of the Soviets coming to the table with the Nazis still running Germany. The Soviets are nonetheless hobbled and the Germans are overstretched and as such a military solution for one power or the other isn't feasible either, thus ensuring that Hitler has his vaunted perpetual war to ensure the continued resilience of the Aryan race.C. J. Samson's book Dominion, while a bit 'you see, the SNP are Literally Fascists' at times, does make the good point that since the war between the Slavs and Poles and the Nazis was one where the Slavs and Poles would be exterminated if they lost, the war could not really end while a Slav or Pole was still living, and every Slav or Pole had a hell of a reason to take up arms.
Hence, the new Eastern Territories would be in a state of guerrilla war near-constantly. I'm not sure his description of it as 'Vietnam on a continental scale' holds, but it certainly would be very unpleasant to live in for the next 20 years at least. You'd have to pay people to take up their Lebensraum.
In one way this would be a triumph of Nazi ideology as it prevents the sort of moderation that @Elektronaut mentioned, ensuring the hardliners maintain the reins long after Hitler himself does the world a favour but it also means that Germany will never truly exploit the potentially vast wealth of the conquered regions, let alone colonise the area in what would only lead to a series of Zamosc style flops.
Basically, unless the Soviets throw in the towel or the Slavs just mutually decide to stop existing Generalplan Ost was always going to be a nightmare rather than a reality. Economically this actually means things remain a bit more rational than turning all your engineers and skilled labourers into soldier-farmers but it doesn't solve the fact that the economy of Nazi occupied Europe was already close to burning itself out in 1944 OTL without having to feed the Ostfront in perpetuity.
Can the situation sustain itself into the sixties? Yes, but it's not going to be the Fatherland world of photocopiers and minibreaks to Zurich, it's going to be Kim Jong Il's DPRK.