Katie,
I am so sorry for your loss. My father-in-law passed away a month ago and my AS was able to attend the funeral but since he is currently in prison, it was with a guard escorting him.
I am sure your son does feel guilt but try not to worry about him. His HP is with him and He is watching over him. Your son has to come to terms with this on his own and hopefully this will be a step towards sobriety for him. Our addicts don't follow a straight path but it is times like these that bring them closer to "their time". May your son's miracle be just around the corner.
Hugs and prayers from one Mom to another,