honestly .. nein.. I mean they could I guess if they wanted too.. but I don't think the locals want to join the USAcant wait to read the history book about the expats that returned to conquer their former home then incorporate it into the nation they left for.
Very, very implausible. USA wasn't anymore expansionist in this point and it wouldn't had do anything from territory in Europe and it would had been against US foreing politics, I think. Even from Japan USA didn't take anything else as some Pacific Islands. And Germans wouldn't be very happy about that and probably USA should expel most of Germans which hardly would looks very good at least in coming decades.
Why would they expel the Germans if there was no one to replace them with? Aside from German Americans I suppose--a lot of people displaced by the Dust Bowl were Volga German immigrants to the US (and their children), so I suppose the US could boot some Germans from their land and place these displaced Volga Germans there.