I don't think there's an easy solution - especially in situations when you have to care for someone whose condition makes them not want that care. In Terry's case, it might mean regular visits to him and his parents by someone who can provide proper medication and counseling, and the social support to plan for his future when they are gone. And maybe providing some sort of boarding in an environment that would allow him to express his gifts. We chuck our kids in schools and our elderly in nursing homes, so maybe there's a way to take care of our mentally ill as well.
All expensive and complicated proposals, I realize, and all dependent on the right people with the right motives to exercise them.
Obviously I don't know the full extent of Terry's family situation from a few videos, but I think it's safe to say living on the streets until he's thrown in prison isn't a fair path for him. And yes, I know that life ain't fair. That doesn't mean we can't try and make it a little more so.