I am half stuck on self-destruct mode, been like that for quite some time. I was horribly, terribly depressed at some point, got suicidal and it went so far that I had a few attempts. When a person truly decides that he wants to die and figuratively speaking pulls the trigger, I'd say that is sort of a turning point because you just willingly overrided your hardwired will to survive, even if the attempt doesn't succeed. I feel it's somewhat indescribable how it feels and what goes on in ones mind when this happens, the memory though is both scary and beautiful (after all, it was supposed to be the ultimate relief to end all suffering, beauty makes sense no?). Anyhow, it's like I got rid of some barriers/inhibitions regarding suicide which naturally led to a total of three failed attempts. Even if the first attempt was half-assed as in I was 15-16 years old and took something like twenty oxazepam pills, at the moment I was sure I would die from this "overdose". Ofcourse I survived. The psychological ramifications of this event however, were of much more importance. I now knew that in me I had the capability of killing myself, all I'd need was a gun and I knew 100% I could pull the trigger easily. If it weren't for outside intervention of friends, I'd be dead long before I registered here.
Actually now that I re-read what OP wrote, I'm not sure if he's even talking about suicidal tendencies but just destructive behaviour. Hopefully I'm not derailing your thread, I just try to help others understand.
Anyway, fast forward to present day, I'm not nearly as depressed as I was back then. In fact right now, I don't feel depressed at all because I'm happy and content with my current life situation. I still have a rather strong desire to die however, like some kind of left-over from the worse days. If I had the chance to do it painlessly, I probably would. To me it's just like going to sleep and never waking up, I simply see nothing bad in it. I know it will case a lot of suffering to everyone I know, but I feel like this suffering comes from a lack of understanding. People who cling to life no matter what are usually afraid of dying, they don't understand how someone could possibly want to die and somehow blame it on themselves, even though they sure as hell can't be held responsible for what life is. I could babble on about free will and what not but that'd only accomplish proving that I have too much free time to think about stuff that eventually makes most people go mental.
Perhaps eventually this desire to die will subside as enough time passes, perhaps not. One thing I know though, it won't happen over one night. If someone has gone on a self destructive rut, you're going to have to make them love life again for them to stop destroying themselves. Try to get away from the things that cause suffering even for a moment (not always possible), try and have a talk with this person (about their feelings, be the therapist he doesn't want to see or can't afford), DO something with him that you both enjoy, something that makes him think "hey, that might be fun to do again some day". It's much more harder than I make it seem, but eventually life tends to prevail because survival is hardwired in us.