At the beginning of their relationship, the victim is love-bombed. Once the narcissist knows the victim is hooked, the devaluation stage begins using strategies such as isolation, triangulation, sabotage and gaslighting.
The devaluation stage is followed by the discard. When you have something that no longer serves its purpose, what do you do with it? You get rid of it. It is with this logic, and as much compassion, that the narcissist disposes of their victim when they no longer consider them useful.