You can shield yourself from his reaction. Send him an email stating that you had a miscarriage. If you wish, you could say you are telling him as a courtesy, and you do not wish a reply of any kind.
I think you are right that he will feel happy about the miscarriage, since he did not want the child. But he might have the sense to commiserate with you, or he might not. You can predict better than any of the rest of us. But you do, I believe, owe him the news, and within the week. You do not have to look at anything he has to say in reply, and you don’t have to take his calls or read his letters and if he should show up at the house, you don’t have to let him in.