It's the old case of the algebra of necessity as Terry Pratchett called it in his books.
It would have been best for the parents to let the child go when it first became clear he was essentially a lost cause, grieve, and then move on with their life, perhaps have another child, and love them and raise them as a happy family. Sad as it may be, people lose children, have miscarriages and still births on a daily basis, and the world keeps on turning.
By clinging on though, not only have they denied their child a peaceful life and death, but they're steadily denying both themselves, from what I gather a happy healthy couple, and any future children they may have a chance at a happy life.