I've done a little homework, so I know the trope isn't really that simple or maybe even accurate. BUT. For those Nazi's that were barons(or any other such nobility) who might have fled Germany/Europe after the war, what would have happened to the barony after they "disappeared?"
I'm working on a character history and was planning his grandfather to have been a Nazi and a baron who went into hiding and was wondering what would have happened to the barony to determine how it might affect the rest of the story. If its just sitting there, open, I would have him go claim it if he can.
Strictly speaking, there were no nazi barons or baronies in WW2 since both Germany and Austria abolished nobility as a legal class after WW1. So a hypothetical Klaus, Baron von Schnitzelwiener in 1945 would have the Baron as part of his name (in Germanyt) and others of his former class would probably still regard him as a noble but there were no legal ramnifications from this, he is a citizen like any other. For your story, well, since the Barony in question is normal private property there are several avenues. If your Baron lived outside of what became the (western)allied occupation zone then his land was likely dispossessed/confiscated after the war. Otherwise his inheritors got it or if there were none, the state.