ibsen s a doll s house

Ibsen very reluctantly acceded to a request for an alternate ending to a German production. In the new ending, Helmer forces Nora to look at their sleeping children and reminds her that “tomorrow when they wake up and call for their mother, they will be—motherless.” Nora “struggles with herself as the play concludes by saying, “oh, this is a sin against myself, but I cannot leave.” In view of the fact that this last act moves toward a happy ending, what is wrong with this alternative ending?