That's a very hard decision ! You have to know if the dog is in pain or having a hard time ! I wouldn't wait till nature takes it's course if the dog is in misery . Hard , painful decision , but I think I would put him down to end his suffering ! All dogs go to Heaven ! Good luck and Best Wishes ! I've been through this a few times myself !
That is a very personal decision! If the dog is in pain, or the disease is causing constant discomfort, then you as the pet owner, have to make that decision!! The dog can't tell you!!!! I've been there, and it is very hard. God Bless!!