About Face and the demons of Tartaros
Actually even if the demons are created by Zeref's magic, they will not die as they are not magic objects but actual living beings. He created these living beings using his Living Magic (Seikatsu Mahou), thus breathing life into them which means they no longer need his magic to continue living. Thus, when all magic will disappear, they will continue to live and their curses won't be affected.