> had they not saved it somewhere safe?
I had to delete 2 user accounts because they hadn't saved the key at all. All others had saved and were able to recover access. However, most didn't even realize they had saved it until I asked them to check their phone storage. A normal user would do anything to get past dialogs and popups, including clicking on random buttons.
1. Either the key is only as secure as what ever random online service you have it backed up on (in which case, it might as well be stored at SN and save the user all kinds of headaches)
2. The key isn't backed up, and this won't be realized until the worst possible time.
2. True but there are a couple of things you can do: i) regularly remind the user via email and in-app notification to backup their recovery key. ii) force the user to download/copy the recovery key on login/signup.
By force, I really do mean force. Don't let the user use the app until they click the download recovery key button.