Perhaps you are misdiagnosing your friend. Have you considered asking them about their history?People who develop DID (the sybil variety) and DDNOS do so to protect themselves from severe chronic trauma, usually of a sexual nature. It must occur before the age of 7 or so or else it seems that the mind is after that unable to 'split'. They also are usually of above average intelligence. The resulting 'mental disorder' protects their inner, unprocessed feelings because they occurred at a time when the person was too young to make sense of them and process them adequately, or because they were simply unallowed or had no time to do so. Most of us cannot fathom the kind of trauma it involves to get here (watch sybil and see what I mean), so it is not hard to imagine a toddler, baby, or young child not being able to process it.
So, the emotions that would result from the sequestered feelings are stopped, because the feelings are stopped because they are locked away in compartments as @sprinkles described so well. Consequently, what these people are most at risk of are what I would call asocial disorders...things that protect them from getting close to others because they are afraid of enduring further trauma. They live more in a state of stagnation or withdrawal from life because life has always hurt. In doing this, they live on autopilot and are stuck in survival mode always, and most deal with PTSD on a daily basis (because PTSD triggers unconscious arousal) they are protected from the feelings that are buried in their mind and body (lots of 'bad' body memories, probably more so than mind memories like most people have, or can even understand), and are therefore protected from the emotions resulting from that. Everything is sublimated to survival. However, it's been said that they have huge amounts of buried rage.
Those with antisocial disorder are more conscious of having been hurt and are more consciously angry about it, but don't know how to deal with it, so they learn dysfunctional coping mechanisms that to us seem irrational, but to them make sense, usually aimed at unfair targets/society in general. They must get a sense of relief--because they constantly are dealing with the emotions but don't know how to release them--when they project them or take them out on others. They have also been traumatized chronically from a very young age, but instead of compartmentalizing feelings that are impossible to make sense of, like in DID and DDNOS, etc., they are forced to deal with them. They then can become so desensitized to pain that, in this process, they also do not adequately develop their empathy for others, which makes all the difference. Empathy for others, in the absence of love and in the presence of pain, develops one's conscience. Therefore, they lack a healthy conscience. That is why it is hard to treat them because you would have to go back, I'd guess with intensive and persistent regression therapy, including hypnosis (I'm not usually an advocate of hypnosis but I think in this case it would be necessary), to awaken or retrieve the infantile feelings of empathy, and bring them to life again.
So people with DID, DDNOS, etc., usually just are at risk of hurting themselves because they become so fatigued fighting to protect themselves and their pysches, in addition to living a dead life, that they have high rates of suicide. Those with antisocial disorder are more at risk for harming others, in various schemes, or homicidally (from your con-artists to your mass murderers). Those with antisocial disorder usually do not have DID or DDNOS because if they had, they might not have become antisocial....Though those with DID and DDNOS, etc., can have some characteristics of antisocial disorder, they have largely been protected from the thrust of it, and struggle more with asocial disorders. Because buried deep in their core are all those unexplored and protected feelings waiting to be opened up.
Thanks so much Sprinkles for your input. I'm fascinated by multiple personality disorder. Please feel free to criticize my post and I will correct as needed.