In our timeline, planning for the resistance was late and not well handled. In this timeline, Heydrich handles the planning. Large caches of weapons are prepared. Underground bunkers are set up to house the leaders of the resistance.

From publicity material: What is V-E Day didn't end World War II in Europe? What if, instead, the Allies had to face a potent, even fanatical, postwar Nazi resistance? Such a movement, based in the fabled Alpine Redoubt, was in fact a real threat, ultimately neutralized by Germany's flagging resources and squabbling officals. But had SS Obergruppenf&uoml;hrer Reinhard Heydrich, the notorious Man with the Iron Heart, not been assassinated in 1942, fate might have taken a different turn. We might likely have seen a German guerrilla war launched against the conquerors, presaging by more than a half a century the protracted conflict with an unrelenting enemy that now engulfs the United States and its allies in Iraq. How migh today's clash of troops versus terrorists have played out in 1945? That scenario comes to life in The Man With the Iron Heart.

(Source: Del Rey)