From someone who has been there I can say that being directly involved with the chaos of active addiction was more than enough to send me over the edge, had I not found Al-Anon and this site. The stress experienced is tremendous....but ...I learned that a good deal of it was due to my own choices. I had to learn a better way both for myself and for my adult son.
It sounds like his parents have had enough of things and are detaching for their own well being. I've had to do this myself and in fact...when I changed my behavior my son was forced to learn to take care of himself as any adult person should. Up to that time I would bail him out of trouble and actually enable his destructive lifestyle---all the while just meaning to 'help' and provide him support.
Keep reading and posting because there is hope and lot of people here who will share what we call ESH- Experience, Strength and Hope.