So sorry to hear about this situation! My heart goes out to you... But like said above, there really isn't anything you can do if he just keeps refusing "help". I realize that his age is fragile and his condition exasperates that, but it is his life and he seems determined to make his own decisions. He must be feeling a lot of pain to be trying to hurry the rest of his life on...
I do know this: whatever HE chooses, it is not your fault. For whatever you are able or capable of doing... whatever you have done, and might not do.... his choices are his choices, and they go beyond your control. I hope that you can feel that when it is needed. (((hugs)))