A danger to others and himself? How exactly? What has he been doing/saying? Has FIL elaborated? Instant diagnosis of PTSD from 5 minute appointment with GP - yes? And no further exploration of this, because your H doesn't want to - no therapy, oh no we don't need that. Some pills might help everything 'blow over', do you think? What does 'all over the place' mean?
Basically what has been sanctioned here is - no attempt to provide a proper explanation of this behaviour for YOUR benefit, no intention to employ every option to make DAMN SURE what has happened here is INVESTIGATED, SORTED OUT, so you have an explanation for his behaviour as well as making sure nothing like this is ever presented to you again - oh no - this will only be addressed insofar as he wants to address it? So it's ALL about him, and not what you have gone through over the past few days?
PTSD or not, the fact also remains that he has treated you appallingly. Goodness knows whether you will be able to put it behind you. I think a reasonable response to this would be, 'I'm sorry, but after what you have said and done over the past week, you do not have the option of refusing therapy if you wish me to consider staying with you. You have an obligation to do absolutely everything in your power to convince me that you realise the gravity of your actions and what effect your statements had on me and our relationship - and even then, this is going to be a struggle. If you think you can go to the GP, get a quick prescription for depression and then come back and everything will be as it is, you are very much mistaken.'
I hope that you also make PIL aware of this - I would guess that they will be relieved that 'something' has been done - I'm sure I'm not the only one on here however that will be raising an eyebrow at this situation. Refusing counselling - yes, that's what he did as all this kicked off. I don't see anything to really celebrate here.
It's clear that the stress of this is affecting you physically too and I hope that you can stay as removed from all of it as possible - get good sleep, stay away from him, enjoy the children and try not to think about it. Don't even entertain the idea of him coming back to the house right now and make sure that PIL know that a bottle of tablets won't undo the damage he has done here.