Is he in the will? :) :)
If it were me, I'd send him a note with a copy of the obit. (Of course, nowadays, I guess it's an email with a link.) He should be told, but he must be aware that his mother is 96. If it meant anything to him, he would have made an effort.
Something I've been meaning to ask ... BB, you have mentioned "getting the call" a few times. Do you not want to be present? Some do, some don't, I'm not judging, but you might give it some thought.