The original poster mentioned MMII, because he wanted to know if the entry for the banshee in MMII had anything to say about her wail having the Death descriptor.
Here's the MMII entry for the banshee's wail:
Wail (Su): During the night, a banshee can loose a deadly wail. This attack can slay up to eighteen living creatures within a 30-foot spread centered on the banshee, or within a 60-foot cone extending from the banshee, at the creature's option. A successful Fortitude save (DC 26) negates the effect. Once a banshee wails, it must wait 1d4 rounds before it can do so again, and it can wail no more than three times per day.
I agree with the others: Death Ward protects against Death Gaze and Wail since both are "magical death effects." Supernatural abilities do not function in antimagic fields so that would seem to imply that they are magical in nature (as opposed to extraordinary abilities, which are not magical in nature).