Remember that you don't actually 'kill' the Nightbringer: he is a god. You shatter the Necrodermis that contains some of the Nightbringer's essence with the instant kill, but the essence lives on and returns to the Tomb World to inhabit another form.
i know but in TT he still should be, if i collected necrons i would be well pissed off if someone killed my night bringer with a crappy force weapon
W:9 D:0 L:0
W:21 D:2 L:3
If you want peace.....prepare for war!