I am so sorry for your loss. What an awful situation. Yes, I would definitely respond, thanking him for letting you know. Maybe, also asking him to pass on your love to the children, and to let him know that he's in your thoughts (however useless he was when she was ill - some men, sadly, do not suddenly step up to the mark; I've seen several go to pieces and completely let their sick partner down). Bear in mind that you are sowing the ground for any future meeting with your grandchildren. he may well relent. His girlfriend, if she is a decent person, may well encourage him to allow the children to contact you - don't give up hope. Also, he must not be allowed to be able to tell the children that he contacted you and that you ignored the letter. Keep it sympathetic and kind - no matter your other feelings towards him (quite rightly). He has lost his wife and his world will have fallen apart. He may well realise that he could have treated her better when she became ill - and feel guilty about that. Definitely respond and don't give up hope re your grandchildren - it may take years, sadly, but my guess is that they will contact you as soon as they can.