What should the old man do if he doesn't follow the doctor's advice and insists on superstitious remedies?

First, you should change your attitude. The old man sometimes looks like a child. Your simple reasoning and facts are not very effective. If your mother stubbornly doesn't want to be treated in the hospital, you can "take the initiative" to find some treatments for her, which can be some common Chinese medicine prescriptions, which are mild and have the best nourishing effect on the body.