I cannot speak in general, but I in person do know several people here in Austria who have been detained in sowjet POW camps until 1955 (26th October end of occupation of Austria by allied forces US USSR England France) but that did not allow them to return from Siberia as they had no Austrian passports due to the Anschluss of 1938 when Austria seized to exist as a nation (!). Thus the Union of Socialist Sowjet Republics did not allow these prisoners to leave Stalin’s empire for their home country but only set them free from the POW camps and had to look for themselves (mainly in far eastern Siberia, working in mines, etc) until they had earned enough to pay for the long way home and apply in the western USSR for an Austrian passport.

That one I don’t know. The anecdote that seems to be mentioned (which nobody seems to be able to verify) is that in at least one instance a former POW that was granted freedom decided to stay in the Chernihiv area because all of his family members were killed. That would of course be an abnormal case. If this is to be believed, there were still 29,000 POWs being held in the USSR in 1950 though.