Considering the year you have had, it is very understandable that you would be so focussed on your son's safety. Your concern is another facet of my concern for you - you've had an appalling time and there is no way you could be sufficiently over it yet, to be able to cope with all this upheaval on your own.
However - I am a pragmatic person. Just because my focus was on the issues you raised and not on the emotions you expressed, doesn't mean I don't 'get' you desperate you feel. I also do get it. But if I express it too, it isn't really giving you any help. It would just be one more person (me) wringing my hands and not actually HELPING.
Although I do acknowledge I'm probably not able to help as much as I'd like. My personal knowledge of boot camps is likely to be less than yours; difficult child 1 was sent to one for a week and from what he told me, I think it was probably a picnic compared to the sort your son is on.
So because I AM a pragmatic person, please do not feel offended or dismissed if I seem detached - it's just me trying to think of practical ways to deal with the issues you face. If you need to, blame it on cultural differences - we are a pragmatic people. Consider it the Aussie version of the British "stiff upper lip".
I am going to try to summarise your concerns. Correct me if I'm wrong.
1) Your son attacked you physically. You had him hospitalised - you were scared for your safety, but you're also scared for his.
2) It's been a bad year for you both, emotionally. A lot of turmoil, a lot of upheaval. Without comparing what you each have been through, you ARE both dealing with extreme grief each in your own way, which also means you each are LESS capable than is usual of two grieving people, to support one another; you each have issues over this that are too difficult to fully express to each other. For example, you have lost a twin who you felt was your other half. He has lost a favourite aunt. Two very different concepts.
3) All this upheaval, plus possible medication issues, plus anger which may or may not have been part of the grief/trauma issues, could well have triggered his outburst.
4) There is past history which is making you deeply afraid for his safety. On top of this, there is your current grief plus your very recent experiences adding to your own fears for him. At this point I express concern for you - here is one big area where it is VERY difficult for you to see this objectively. You may be very right to be concerned - or you may be over-reacting. Or anywhere in between.
5) Your son was placed in this 'boot camp' (for want of a more accurate term). And almost immediately, the rules change and you're told he won't be able to stay past 18. And from the sound of it, these sort of places don't expect to throw them out with that sort of a deadline (I could be wrong here - as I said, correct me if I am). So you are concerned that he will be ejected suddenly with no provisions made for his placement or his care.
Please tell me - how likely is this, really, to happen? Again, I could be wrong - maybe this DOES happen. But from my understanding - it shouldn't. It would be immoral, to say the least. As I see it, they have a duty of care, having taken him in to this extent, to at least give a hand over when he leaves. I mean - even if you go to the emergency room at the hospital for a cut finger, you get a hand-over when you leave, in the form of a letter to your regular doctor. Or doesn't it happen this way in the US?
So, looking at it practically - if he has to leave when he's 18, it seems to me they would be legally responsible for him until he is given an alternative placement, or released with someone delegated to supervise (through follow-up) where he goes and how he lives.
Now, it IS possible that someone thinks that YOU will be where he goes and who takes over his care.
So here is where YOU need to do something (and I think you already have) to make it clear that coming home is not going to be a satisfactory option. It would be putting things back exactly the way they were before, when he attacked you.
5) Now, almost in contrast with the previous point - on the one hand, you are concerned they will toss him out on his ear when he turns 18, but on the other hand they are getting in touch with you and telling you he is "unmanageable" - this is interesting. And I think could actually be a good thing for him, and for you. Because surely it means they are LESS likely to throw him out? At least, not without making sure he and you are both safe, and that strategies are in place.
Have you specifically asked them what happens for him from here? What do THEY say happens when he turns 18? What about if he continues to be a problem? What about if he dramatically improves? What do they intend doing with him, in each of these possibilities? And with each of their answers, what do you feel about them? And will you be safe, but still able to have the contact with him at the level you want? Is there anything practical you need to know about, to begin putting into place?
medication issues - that is entirely out of my experience, other than friends going through similar problems. But what has been said is true - it is up to him to take any medications prescribed, once he is out on his own. Getting him stabilised now won't do any good if he isn't motivated to keep taking medications.
You mentioned something about an advocate for him - is that a possibility that someone could be found (other than you) to be his advocate? I do understand the problems of having offspring who can be legally adult but in other ways cannot function as one. If someone could be found to take on this role, it would be surely something that would be useful for you? It could provide another string to his bow, at least.
Also, is there any possible advocate for you?
I still think you need to use the time he is away, to get some help and respite for yourself too. You need to be good to yourself (and maybe find someone else to be good to you) to help you in your own recovery from the ghastly year you have had.
Marg