So, since the latest patch I didn’t have any of the old host migration issues. I don’t know if the old behaviour is still possible and I just haven’t played enough.
What I did have are three scenarios:
a) I am the new host. Returning to Keep. Getting all the other players.
b) I am joining one of the other players (his name is not displayed normally, but rather as a code of some kind). There is no “Cancel” button anymore, just “OK”, i.e. no choice but to wait or close the game. I end up in his keep.
c) if there were four players, b), plus the new host closes the game or something, and either a) or b) between me and the last player.