this story does not have a happy ending. Herbert is not coming back, and Mr. and Mrs. White are left childless and grieving.
I think that we can infer that both Mr. and Mrs. White think their son is at their door in zombie form.
It is not clear what they will do about the knocking at the door. It is possible that Mr. White might use his final wish to send his son back to the grave. Mr. White cares for his wife so whatever happens depends on how Mrs. White reacts to the noises outside.
