I would say, oftentimes, the narcissist's biggest fear is that you might move on and thrive without them.
The thought of this often worries the narcissist more than you smearing their name or exposing them. The thing is, the narcissist knows you have the ability and potential to pursue true happiness, fulfilment and well-being. These are things the narcissist can never have.
So the thought that one day you will most likely be doing better than them and without them, causes them a lot of emotional anguish and pain. This is the main reason they are so jealous of you. They know they cannot have what you can easily have. And this is the exact reason why the narcissist tries to bring you down so bad — to keep you so distraught and devastated, that you might not be able to find personal happiness and fulfilment.
And they will do everything in their power to do this to you. They want to keep your mind and judgement so foggy and impaired, that you can't follow your own path to fulfilment. Hence, after you are gone, the narcissist does calculated things like: ‘hoovering' designed to pull at your heartstrings, or ‘smearing' your name. This is to either keep you down, hooked on the idea of them, or both.
Once more reason to block them out completely.
And thrive.