Since you've already exposed the A to them I'd say you've done your job. It's his now to tell them he moved out. Perhaps it's just wishful thinking from the mom - hoping since she hasn't heard anything that all's ok now.
You could send it back - return to sender - but that's a little cold if you've had a good R with her in the past.
I'd leave it in the pile of mail if you've already started one for him.
You could throw the pile in the litter box.
Me 56 H 47 Married 21 years No children Bomb & moved out 4/07 "My feelings have changed" & "I want to live by myself". Ow Bomb 8/07 H filed 6/08 D final 2/05/10