Indeed, that app treats each user individually and since an app would have to actively sync up some deactivated (or even deleted) user state explicitly, which releasebell does not, it just keeps working for that user.
Since the app uses OpenID, there is actually no real way for the app, to know if a user even still exists to then purge the user. A login of the user would of course not work, but since this works in releasebell without a login-session, not sure what to besides manually purging that user.
Have to think more about how to better handle that, until that you may have to actually do what you proposed. I was trying to quickly come up with a mysql statement to purge, but that is more involved than I thought, due to all the constraints.