The wish did make Herbert come back but it wasn't the Herbert they once knew. Mr White knew that their son wasn't the same and he knew that a consequence comes after every wish so he made a new wish before Herbert was inside the house
"The door won't open! I can't get the door open!"
Mrs. White finally got the door opened and she raced outside into the darkness. She began to sob when she realized that Herbert wasn't there. One year passes and Mrs. White passed away. Her husband later died as well in front of her grave. The monkey paw was left out in the open for the next unlucky person to discover it.