My goodness that would be terrifying and heartbreaking for you! While it is possible it could be some kind of premonition , I wonder if it is worth him exploring other options as well like his mental health, possible depression etc? I would be accepting of his feeling,s but also gently encouraging him to explore all explanations for them, you know? The mind is such a powerful thing when it comes to health, even people who have a legitimate diagnosis of terminal illness benefit from a positive attitude & faith.