This is what always happens with severely responsible and talented people who take pride in the quality of their work and apply themselves hard, regardless of the rewards and recognition, material or otherwise: They do an extraordinary job in every function they are assigned, they show initiative and undertake tasks beyond their scope of responsibility, they set their own lofty goals and high performance standards, they pull off feats of creativity and miracles of ingenuity. Truly they accomplish things that no one else would in their place.
More frequently than not they don't run around screaming about their achievements - after all, they simply cannot operate any other way and they don't care that nobody asked them to be like that. They themselves know that they are the best. Plus, people around them acknowledge such efforts in one way or another - subordinates show respect, peers get testy, etc. And the bosses? They either don't notice anything, because their heads are usually up their asses, or they are too limited to appreciate the ace-level pilotage they are witnessing.
As someone afflicted by this condition, I can assert that there is nothing healthy about it. Privately wallowing in the knowledge that you are "simply the best" and that your work ethic is a cut above everyone else's, while not being adequately rewarded for your efforts, is nothing more than an addiction to one's own ego. It's vanity of the worst kind, because it violates the principles of objectivism and merit-based recognition. And, like any addiction, it is accompanied by a couple of supplemental attributes.
One of them is the inevitable development of passive-aggressive behavior: no matter how many times a person is going to say that she does it for the sake of her own self-satisfaction, something deep inside wants to be celebrated for the extraordinary abilities, efforts, and results. This secret desire is in a constant fight with an extreme dislike of boasting. Thus, the feelings and impulses get mostly suppressed and come out in the form of classic indirect hostility and resentment.
Another attribute is the illusion of irreplaceability. The tormented crazies convince themselves that without them the company will not be able to survive; that everything will fall apart and go to hell. They believe that there is no way somebody else could be found to fill their shoes. And why not? Nowadays, people like that are quite rare. It's most likely that, if an employee in question leaves on her own accord or is let go for some reason (because she becomes unaffordable or her attitude becomes unbearable), the employer will never ever have someone that good in the same position. But does it really mean that losing these truly invaluable workers is an incurable disaster? Are they really irreplaceable? Let me answer this question by doing what I frequently do - relating the readers to an example from popular culture.
In case you have not had a chance to check out the Netflix/Lionsgate's co-production Orange Is the New Black, I urge you to do so - trust me, you will not regret it. The show's creator, Jenji Kohan (widely known for her Showtime offspring, Weeds), is a member of a still rare breed of entertainment developers, who is able to focus on female characters without reducing the finished product to gender-specific genres. Orange is the New Black takes place in a women's federal prison, and its ratio of male to female characters is about 1:10. Yet, 47% of IMDb users who rated Orange is the New Black (8.5 stars overall) were males.
One of the primary characters in the first season of the show is an inmate of Russian origin, Galina "Red" Reznikov (Kate Mulgrew). This formidable woman runs... no, she rules the prison's kitchen and has an influence on pretty much the entire social canvas of the place. By the show's start she has apparently been there for years and assumed a role of a Godmother for a tight circle of her "daughters." She can be a real bitch, and a newbie should think twice before contradicting her. But the truth is she is doing a remarkable job, keeping her fellow convicts and the staff fed and even rewarded with treats under the conditions of ever-shrinking budget, broken fridge, and oppressive hostility from some nasty guards. As early as the 5th episode, it is impossible for the audience to imagine the kitchen without Red. Obviously, she herself thinks she is irreplaceable.
Guess what? Towards the end of the season, the combination of some people's foolishness and others' unsavory scheming gets her kicked off the throne and out of the kitchen. So, what happens? Do the lights go out in the mess hall forever? Do the prisoners get shipped to another facility to be fed? Nah ah! Another head cook is found right there in the general population and installed in front of the range; she brings in her own crew; the cooking continues somehow. True, there are no more yogurt favors, the menu is severely skewed towards Latin-American cuisine, and even the oatmeal comes out spicy. But the plates are not empty, people are not starving. Life goes on, while Red is driving herself insane with displacement anger.
So, the answer to the above question is: No, you are not irreplaceable. It may take a whole team of less adequate and more expensive people to pick up your tasks. And collectively they will accomplish less and it will not be brilliant, but it will be just good enough for the business to continue, at least in the short run. Let me assure you that nothing will fall apart, because doing things half-assed and with little care has become a widespread norm. Everyone accepts poor quality at a higher cost nowadays, and so will your bosses. And you, with your talents, skills and unsolicited attempts to jump over the high-standard bars, are just an ego freak.