Very good point about the sheath and one I was going to make. If something as powerful as Nightblood, which can drive men to kill, and be stopped (for the most part) by being fully sheathed, is the sheath a separate Awakened object, part of the same object somehow, or a different magic entirely?
Also, as for a Lifeless viewpoint character, I think it would be very similar to the monster, Hunger, made of earth in Servant of a Dark God by John Brown. It was sentient, but didn't really have memories or feelings, only a hunger for souls. It acted very much on instincts and didn't have much humanity. I won't go into further detail for fear of spoiling a book which we aren't even discussing. Just my thought process.