Facebook login

I'd like to buy Facebook login:
http://www.opencart.com/index.php?route ... ok%20login

1. if i have 2 opencart shops,do i need to pay twice?

2. if someday Facebook changes the login web source and "Facebook login" didn't update, what i should do?

1. If you are running OpenCart multi-store, you will only need one license. If you have 2 separate OpenCart installation, you will need 2 license since OpenCart's license is that one store requires one license.

2. The extension will be updated accordingly if there's a change in Facebook's API.