Ok. I'v tested to see what happens if a user removes the app from his FB profile after register on my site with FB login option.
1. The user data remain in my database
2. I'v come back with the same FB account (after removing the app) and tried to login again with FB and i recived this http://i47.tinypic.com/2dminwg.jpg
Maybe i haven't set the FB app correctly.
I'v searched the internet and find that i must enable Reset Client Token.
I enter the FB app that i'm using for this & click Enable & Save. After clicking the Save button, the Reset Client Token goes to Disable.
I don't know if this is the right thing to do, thats why i'm asking for help, to resolve this issue.
I want, if a user come back after he removed the app from his FB profile, to have the permission to login again with FB option and to not create another user on my database. I want him to use the same user that he had on the 1st time.