Yahoo says it is discontinued.... IS IT ?

[Philip]

The account could have been disabled because the mailbox is full and can't accept any more messages. Also, if the Yahoo account had not been used in a long time, Yahoo may have disabled it and your friend can no longer use that email address. Yahoo recently announced they were going to delete "inactive" accounts that hadn't been used for a period of time, unless the owner of the account responded to their alert. This was and is a controversial practice, for the very reason you mention in the last line of your post. Your friend may still be able to log in to Facebook with that user name, but if he/she needs to make changes to the Facebook account, Facebook will try to send verification emails to the yahoo account, and that will fail.