My understanding is these library definitions are stored in SAS metadata. You can use SAS Management Console to restore from a metadata backup from before you deleted the library. You will however lose any metadata changes made since then. By default SAS metadata is backed up daily.
Select Metadata Manager ==> Metadata Utilities ==> Server Backup to list the available backups to restore from. To restore just right click on the required backup, and select Recover from this backup. You might want to do a backup first before restoring just in case you need to revert.