a) Alpenfestung
As a German I am a little bit salty that Austria often escapes their part of the blame for WW1 and WW2 (don't get me started on A-H's war crimes, A-H nostalgy my ass). The whole "First Victim of Fascism" narrative that Austria constructed after the war, allowed them to retreat into comfortable neutrality. They avoided painful division and (rightful) blame for the horrible crimes.
How would the world view Austria if some form of Alpenfestung is actually implemented?
https://en.m.wikipedia.org/wiki/Alpine_Fortress
SS, Wehrmacht and NSDAP actually use considerabale ressources to turn Bavarian and Austrian regions into a last redoubt. Austria is remembered as a fanatical Nazi holdout and one of the few places were Werwolf activity actually happens.
https://en.m.wikipedia.org/wiki/Werwolf
My guess:
Basically the whole we weren't actually Nazis shtick doesn't really work. Austria is seen as German and responsible for WW2, instead of being a victim of Germany. Austria is probably divided between East and West and Eastern Austria joins the GDR while Western Austria joins the FRG. I don't think we would see the separate modern Austrian identity of OTL.
Interesting ramifications for the Cold War. France, Britain and Russia are going to be really nervous about a reunited Großdeutschland....
b) German Hiroshima
Germany resists longer and the Ruhrgebiet gets a healthy dose of instant sunshine.
My guess: Germany is going to be even more pacifist than IOTL. Maybe Germany isn't willing to join NATO and actively avoids the "Westbindung" of OTL in favour of true neutrality.
c) Operation Valkyrie actually happens. The West immediately accepts a white peace, Germany throws all forces East, the oppressed peoples of the SU are liberated and Rommel is German President in 1950...
No,I am kidding. Hitler dies and Valkyrie at least partly succeds. Obviously it is far to late for anything but unconditional surrender at this point.
This scenario is a little different because there are several ways how a successful Valkyre could actually unfold..
my guess:
The really interesting consequences here are:
1) Possible earlier ending of the Holocaust. Massive butterflies for Israel.
2) Possibly a smaller Eastern Block. Battle of the bulge is not happening. Instead everything is thrown against the Soviets. The W-Allies are probably able to advance much further, while the Soviets are in for a bloody slog.
3) Prussian militarism enjoys more legitimacy than IOTL. This could potentially cause massive butterflies for the post-war German political right. The implications are far reaching. People like Stauffenberg weren't democrats and had fairly extreme views in a lot of regards.
Maybe Operation Valkyrie has some very toxic effects on post-war Germany. There is at least the possibility of a second Dolchstoßlegende.