All lawyers have been at this stage: Either the case is closed or a successor lawyer has taken over. Different states have different ethical rules for how long a lawyer must keep papers before destroying them. But what about returning the file to the client if there is a change in the helmsman? [Well, that was a sexist remark.] What if there is a change of lawyers midstream?
The ABA Journal has a perceptive article on this issue today. You can read it here. The logic makes perfect sense.