It depends on the site. If you run a site that uses Facebook for login, when you log someone in via Facebook, you can ask for their email address via the "emai

It depends on the site. If you run a site that uses Facebook for login, when you log someone in via Facebook, you can ask for their email address via the "email" extended permission. Your site can then support a password reset page (like most sites already do) to enable those users to create a password via email if they decide to delete their Facebook account. Requesting email address is a good "escape valve" for users if you are concerned about this aspect of Facebook login.