A variety of ways to respond.
Put your hand up in stop sign "Talk to the hand."
Plug your ears and sing "La la la la"
Quack like a duck to answer their concerns.
Every time he comes up grab their hand and say, "Let's say a united prayer to cast the demon drink out of his body and mind."
Try to look like you are floating in monk like peace and drone, "Expectations breed resentments", "Let go and let God", "he has the dignity to make his own choices,."
I am sorry to hear this, but how is your son/daughter?
Oh my. Oh dear. Gosh. Golly. The Gallic shrug.
Every time his name comes up I need to take a shot!
Give them your evil eye and say nothing until they awkwardly change the subject.
Do not answer but completely change the subject or say nothing. Let the silence just streeeeetchhhh.
Yes he really has been an unsuitable mate. Do you know anyone not an addict and single?