Watching this episode again today, I get the impression that his family took the diagnosis of bi-polar too lightly, which is not unusual, and they did not seem to think it was a big deal when he decided to quit taking his meds, when it almost always is, Imo. People who have bi-polar can deteriorate very quickly without medication, and paranoia is a common response. This is where I feel they are either in denial, or simply not being informed about the illness. There is nothing to show he was being threatened or was in any danger, something his close friend would likely be aware of, yet they, or at least his sister, believe he was.
I have a brother who first displayed signs of mental illness while away at college. Instead of running, he returned home and basically, in 25+ years, never left again. He refuses all meds, but as he keeps to himself and does not go out into society, he is able to stay safe and not endanger others, though he has never shown any signs of violence. But if he took the route of running away, who knows what might have happened.
I don't get the feeling he is out there, living his life, though. I fear he may be among the thousands of unidentified bodies around the country. He may have gotten far enough away to not be linked back to MA.
His mom is naive in saying he would have told her, told her everything, etc...young people just don't, Imo. Especially if he was having an episode. Anyway, this is a very sad case and I hope the family has some kind of finality at some point.