User blog comment:B214/Light Novel Volume 16 spoilers/@comment-82.40.154.8-20140106171716

i am willing to bet that since valiere's bastard of a brother turned her longinus into a weapon, ui bet Azael goes super-mad super-smart genus mod and uses it to bring her back. There is no way the author would just kill her off  in the same volume as her first aperence.