From my experience having a narcissistic mother and from reading,
Narcissists rarely "realize" they have npd. When their surroundings change and they are cut off from those who play along in the narcissists games and give them supply (in my moms case, when all the kids were gone) they may seek help for depression or anxiety or a raft of other problems. Often the treatment for these things because they are based on building up self esteem and validation merely rebuilds the narcissism as the narcissist plays the therapist to get what they need. They may wear their new condition on their sleeve to obtain narcissistic supply from others, and when they get enough of it, they may continue with therapy even when it no longer seems necessary.
When the last of the kids were gone and living normal lives, my narcissistic mother had a "nervous breakdown" and started getting treatment for depression. This involved a lot of moping around the house and wringing her hands, interrupting everyone elses grown up conversations acting like a child. Unlike my brothers and sisters, i could see it was mostly an act after the first 5 minutes, and once i tuned it out the crocodile tears came without reason to up the ante. Every opportunity to bring up her condition was seized upon. We could be having a conversation about video cables and hooking up a tv and shed find a way to slip her condition into our conversation by interrupting.
Eventually she reorganized her life in such a way that she reobtained supply (by taking in a bunch of troubled foster kids.... Ugh) and started a business and hired an employee who was not capable of doing the work properly (completely on purpose, i might add, my sister could type like a demon and had mad office skills and she was passed over) then she started acting like a normal narcissist, grandiose as ever.
When my sister committed suicide (my narcissistic mother had both of her kids taken away, an had excommunicated her from the family for a tenth and final time), she again saw an opportunity not unlike with the supposed nervous breakdown. She did the hand wringing thing again, put up a shrine to her in the house, talked about her sadness incessantly. She also organized a bizarre highly religious funeral for a girl who had no religious affiliations whatsoever, something that much of the siblings found offensive, didnt give us brothers and sisters an opportunity to speak, and just happened to invite the entire congregation. Now, if your concerned that maybe im being a bit insensitive, this is the same woman who took down and hid all of my sisters pictures, who said she hoped that my sister died and she was just waiting for the police to call to say that she was dead so she wouldnt have to dread that she might show up god forbid, at the door needing help. And she didnt greive like a normal person at all. She greived for five whole years. Made me sick.
So to answer your question more simply, in most cases no. Some may find themselves questioning why they are feeling in a socially unacceptable way (hating their own kids and wanting to kill them or hoping they run away for example) and seek counsel, but most seem to only reach out for treatment as a crutch due to lack of supply and therapists inadvertently supply them in droves. Usually its the kids of a narcissist who realize whats going on when in therapy for something else themselves, and in probing the therapist realizes the root of the problem. I cant imagine a positive outcome though, of an adult child of a narcissist telling their narcissistic parent that their therapist suspects they are a narcissist, i doubt that method would lead to treatment at all, it would probably lead to the narcissist trying like hell to get the therapist on their side so they can triangulate the child through the narcissist, a disaster.