@naphthous: If an external drive gets disconnected, Insync pauses syncing and waits for the Insync folder to get re-instated. It does not consider the files to be deleted.
Is Insync folder set to a root drive (and not a subfolder), say “X:”? When you say the letter is still there, does it get replaced with some “non-empty” folder? Because if the Insync folder path gets replaced with an empty folder, then it doesn’t consider the contents to be deleted and fails to resume syncing creating an “Actions Required” entry for the users.
Please send to us the Insync logs at support@insynchq.com so that we could look into this further.