Some of us may stay in an unhealthy environment longer than necessary because we want to stand strong, and not back down because an adult bully is on the war path. But, depending upon your circumstances, this may be the wrong approach.
If you're being bullied at work, and you depend upon your income, you may have little choice in the matter. You may need to stay until you secure other employment. However, if a malignant narcissist strikes in a more informal venue, such as a social group, a volunteer organization or a religious setting, you need to decide whether you are better off staying or leaving. In most cases, leaving, and finding new friends, a new place to worship or another outlet for your energy, is the best course of action and one that will bring you great peace.
Cutting your ties with a narcissist is a very wise decision. It might be retreating, but it doesn't have to be defeating. You are moving on and making a very good choice not to stay in a highly toxic environment. Usually, by the time you realize anything is wrong, a narcissist has already poisoned the atmosphere. These very disturbed individuals do not strike until they manage to erode any support you might have once had. They will patiently and painstakingly work to make sure this happens. This is why the situation has turned toxic. All of your friends and acquaintances are forced to choose. Will they support you, or will they back the bully? If they choose you, they realize it will cost them. The bully will not forget, and she'll probably target them next. Most people do not possess the integrity to do the right thing under these circumstances, especially in the workplace.
Basically, when a bully goes on the offensive, you're a sitting duck. But retreating is not a sign of weakness. You are walking away from an unfair and non-winnable situation.. You are distancing yourself from people of weak character. None of these enablers are morally sound. Only a person with a cold heart will watch, and do nothing, while someone else is kicked around.