As the disease porgresses, they lost interest in eating. They forget to eat, and how to eat. And one factor is, they have difficulty in swallowing. Since they stop talking, their throat muscle becomes rigid and stiff. No practice, no exercises, until they give-up eating. In this situation, you must give them soft diet, or chopped food into small pieces. Be careful, don't rush, they might be choked, or sometime aspirate.
You must have conversation with them as much as you could. Keep singing with them. this is a speech therapy. 'So they won;t forget talking In between meals give them snacks like sliced apple, or any fruit. Give water more often to avoid UTI, dehydration, and constipation. These will keep them talking and eating.