I found my oldest Angel on the bottom of the tank this morning. By the time I saw her it was too late to do anything; I saw her last breath. It's sad to see her go, as she was one of the fish I started the hobby with.
Although she did pass away, I don't think the Mota was to blame. There was no damage on the Angel's body or fins, which there likely would have been if the Mota attacked her. If more fish die, then I will start to look at the mota as the cause of the deaths. Until then I hope the Angel just died of natural causes.