He won't go through with not seeing the DC, he won't harm himself and he is NOT having a breakdown.
These are the desperate actions of a desperate man trying to win back power.
Only HE can stop this madness, as HE was the one that created it all.
solo didn't force him to change jobs, walk out on her and the DC, this was all down to him. He can weep and wail all he likes, he can pop all the ADs he likes, but until he is able to stand in front of the mirror and face the one that is responsible for all this mess, there is nothing anyone else can or ought to do.
Tell the DC, jointly with the PIL and show the DC that they have bags and bags of support.
Change the locks, LET him take you to court Solo, he has clearly shown himself as unstable, and you are naturally protecting yourself and your DC in case there is any MH fall out.
I speak as former depressive, a suicide survivor, I understand H&Cs comments, but would stress most strongly that denial of contact with the DC is indeed not a good idea IF (HUGE IF) there any truth to his MH issues. But by the same token, the DC need to be protected from it and certainly never involved in his active treatment. They should not see him disravelled and ranting.
Solo needs to use these latest developments to her maximum advantage, to regain and maintain power. Cold and calculating, perhaps, but it is no more or less than this H is trying with his histrionics.