Linked Facebook account with multiple users in analysis

In my application I am using syntax services to connect users to Facebook. When a user tries to connect to a facebook account that is already associated with another user in the app, an error is presented and the user is not allowed to connect. Since I am using anonymous users in my application, this is a particular problem if the user uninstalls the application and reinstalls as their old account still exists in the database associated with their facebook account, but now they have a new anonymous user account and cannot link new account with facebook.

What's the best way to solve this problem? If I am not mistaken, there is no way to tell when a user is deleting your application, so I cannot delete the old user from the database when I uninstall the application. I need a way to either log out of the old user or log in as a new user when the new user tries to connect to facebook, or allow multiple users to connect to the same facebook account. Or am I suppose to merge the new anonymous user account into the old one linked to Facebook.

Anyway, does anyone have such a problem and find a good solution?