Most of them became Heimatvertriebenen in West Germany, which was the name for expellees from the territories beyond the Oder-Neisse Line. They remained a major right-wing group that opposed normalisation of relations with the GDR or the Soviet Union. They seem to have been a pretty big group, given that Adenauer's Social Democrats wouldn't recognise officially the O-N Line due to their opposition. They got around this by continuing to officially claim the territories whilst signing non-aggression pacts with Poland and Czechoslovakia. In fact, Adenauer had to constantly appease the nationalists from the east by talking smack about the Anglo-Americans and doing what he could to help out Nazi war criminals like the Spandau Six.
Some of them are still around in social clubs, I think, but the 1970s saw a big shift as the younger generation of Germans rebelled against their parents' latent ultranationalism and the FRG dropped the claims. Some of the Neo-Nazis in Germany today are probably descendants of Junkers, although I don't think many people care enough to want the land back anyway. Over time people adjust to their reality and end up trying not to rock the boat.