It depends slightly on when the PoD is. If Germany scores a quick victory at Stalingrad, then Fall Blau (Case Blue), their operation to capture the Caucasus' oil at Grozy and Baku, might well succeed. If not, they can still head for the Caspian Sea and cut off the Soviets from Baku which has the same effect. In that event we could see a Soviet surrender ( a la Brest-Litovsk, Version 2.0). Then we got a German dominated Europe vs. the Anglo-American allies. With Caucasian oil, a free hand in Europe, resources from all of Europe, this could be a very bloody affair. Remember the production increases in production under Speer in '43/'44? Imagine that with the labour force of France and the Low Countries, Romanian oil, Ukrainian coal and steel, Soviet grain and an ocean of slave labour. The bulk of the Luftwaffe can now be transferred to the west causing the bombing campaign to be much less effective due to high losses. I'd say that any invasion of 'Fortress Europe' (which is a proper name ITTL IMO) will be a bloody failure except if you try the periphery of Nazi influence. The Americans might well say 'to hell with it' and wait until they got nukes. In this scenario, Germany holds on until August/September 1945 and maybe even into 1946 and 1947 although by then Germany would be a radioactive wasteland. Nuking Germany might well fail in some attempts with a more potent Luftwaffe and all those AA guns not in the east ITTLl, but in the end it won't help.
If we're talking 1943, the Nazis could opt for Von Manstein's 'backband blow' instead of Citadel. That involved luring the Red Army after the desperately reforming Sixth Army in, say, May 1943, into the Ukraine. Von Manstein would then move south from Kharkov east of the Don and press the entire wing of the Red Army against the Sea of Azov, losing Stalin one million men and a lot of tanks. This doesn't knock out the USSR but likely means the Soviets won't reach German territory in 1945. They'll likely reach pre-1939 or 1941 borders. End result => nukage ensues.
In the event of a late PoD (1944/45), Hitler could avoid the Budapest offensive. If we butterfly some bad weather at the Battle of the Bulge, the Wehrmacht might be able to seize those much needed oil supplies and set back the Allied approach for a few weeks or maybe even months. This is only delaying the inevitable and fighting to the end = nukage as well here.
I suppose you meant a guerrilla resistance. There was a plan for a so-called 'Alpenfestung' in Bavaria and Austria. Hitler was somewhat enthusiastic about it in 1945 but the creation of the foundations for a guerrilla resistance by the SS and Wehrmacht remnants would have to be laid earlier (1943?) and I imagine that with lack of local support, except in Soviet occupied areas, resistance would end soon and Hitler would die in the Alps somewhere, commit suicide or get caught and put on trail. Except for East Germany, I don't see resistance last any longer than beyond the first 3-4 years. In the East Germany, especially under harsh Stalinist rule, resistance might draw more support and last well into the 50s and even 60s like it did in the Baltic states although I imagine guerrilla warfare would be exchanged for plain terrorism at some point.