Plugin works great. Nice thing you did integrating Google Authenticator with the WordPress :)
Works as its described, nothing more, nothing less.
There's one suggestion though, in case of lost phone or accidental deletion of account on authenticator, I think we can simply try to integrate your another plugin to the rescue, Perfect Paper Passwords, so that user will have at least some fail safe when such scenario happens. On the login page we can add lost phone option as well on clicking which it will allow usage of Perfect Paper Passwords.