How would Mathilde Loisel break the news to her husband about the necklace being fake?
This is a good question and we must examine the type of person that Mathilde Loisel is at the end of the story. One would hope that she has completely changed for the better and is not as worried about the finer things in life, but the way in which she responds to Mme. Forrestier might lead us to believe differently . She is almost angry with Mme. Forrestier that her diamond necklace (if it were rel) was so vastly expensive. She goes as far as to blame her for her poverty stricken life. We don't get to see much of her reaction when she finds out it is a fake. I would venture to say that Mathilde decides never to tell her husband because of her pride which was what got her into trouble in the first place. She was too proud to go to the ball in anything less than an expensive new dress and, what she thought was, expensive borrowed jewelry. She was too proud to admit to Mme. Forrestier when she lost the necklace. I think that she will be too proud to admit to her husband who has been working three jobs day and night for ten years to tell him that it was all for nought.
A fascinating question. On a simple, factual level, of course, we don't know. We have to extrapolate, and to take an educated guess about how much she has grown through the story.
I would say that her first response would be like the narrative voice's reflection: she'd reflect on how different things would have been. I'd even say she would break down in tears over having lost so much. Then, I'd say she would grow quiet and realize how much she had learned (I hope).