Narcissistic personality disorder, like any other personality disorder, affects the emotions, thoughts, and behaviors of an individual. In particular, narcissists exhibit symptoms such as inflated self-image and self-importance, lack of empathy for others, damaged relationships with others, aggressive reaction to criticism, to mention but a few. According to other individuals, people with NPD are arrogant, selfish, manipulative and domineering. However, deep down narcissists have problems with their self-esteem and will behave as they do as a way of coping with their shortcomings. A narcissistic personality disorder can be managed via psychotherapy, but if left untreated it can result in many complications. 
What Happens To Untreated Narcissistic Personality Disorder?
Generally, people with NPD do not associate well with others. This is because they are incapable or unable to consider other people’s feelings and emotions. One of the complications of untreated narcissistic personality disorder is problems with the individuals work, social and family life. Additional complications of untreated narcissistic personality disorder are associated with their well-being including physical, mental and social health. Physically, if an individual is living with narcissistic personality without treatment, they may experience suicidal ideations, aggressive behavior, and abuse of alcohol and other drug substances.
Suicidal thoughts are usually a sign of worsening narcissistic personality disorder, and if it gets to a point of actually idealizing the thoughts, an individual can succeed in killing themselves. Aggressive behavior in individuals with NPD is common, but it can worsen to the point of physically hurting themselves or hurting their victims. Abuse of alcohol and other drug substances affects one’s behavior and thoughts, even for normal individuals. The effects on individuals with NPD can be worse, and they can do things which could harm them physically.
Psychologically, an individual will likely have low self-esteem issues, depression, anxiety, lack of interpersonal skills and hypersensitivity to insults or criticism. The latter psychological implication can involve aggressive behavior including a narcissistic rage and giving a cold shoulder to whomever, they think is against them. In terms of social well-being, living with untreated narcissistic personality disorder could lead to an inability to create and maintain relationships, decreased performance at work or school, and withdrawal from loved ones.
Individuals with a narcissistic personality disorder do not see the wrongs they do, and if their loved ones or family or colleagues point that out, they are likely to cut them off from their lives. Therefore, it is likely you will find narcissists divorcing their partners or breaking up with their lovers, having poor relations with workmates and family members or avoiding them completely. Also, one may lack meaningful relationships in their lives due to demeaning others who they perceive to be lesser special or unique than they are. 
Identifying A Narcissistic Personality Disorder
Individuals suffering from a narcissistic personality disorder have a compulsive need for attention and admiration based on unrealistic expectations, and a sense of superiority and entitlement. In order to keep up with their unrealistic expectations, they need others to buy into their illusion so as to feel worthwhile. Therefore, they use others without a care in order to boost their ego. However, their actions have consequences which make them vulnerable to any criticism and the fragile self-esteem. Basically, a narcissistic person believes they are better than others, expect constant praise and admiration, take advantage of others, and lack empathy for others. Additionally, they fantasize about their beauty, power, and success, exaggerate their achievements and talents, are jealous of others and believe others envy them and have an idealized self-image of being tough while they are quite emotional.
A narcissistic personality disorder may not seem like a serious condition, but leaving it untreated is not a wise decision. Clearly, there can be grave consequences of untreated narcissistic personality disorder such as suicidal attempts which can lead to death and narcissistic rage which can lead an individual to cause physical harm to themselves and their victim. The best way to manage narcissism is through talk therapy (psychotherapy), to help the patient identify their problem and aid in resolving their behaviors. With treatment, an individual with a narcissistic personality disorder can lead a more enjoyable life and relate better with others.