Ever story deserves a happy ending, but happy is a point of view. To some finding true love is a happy ending, and to others defeating the villain is happy. In A Streetcar Named Desire, written by Tennessee Williams in 1947, they receive both.
In the play, the ending is happy because Stella and Stanley stay together despite his abuse and her sister, Blanche, who was a crayon short of a box. He wrote the play to stir up emotions. What woman would stay with a man who slapped her several times while she was pregnant? What woman would take the side of her husband over her sister--evidently a woman created by Williams? Stella saw that Stanley only hit her when he was drunk and when she provoked it by yelling at him or standing up to him. She also believed Stanley when he had said that Blanche was not who she used to be; she was now a lady with a past that circled the town a time or two. Even though Stanley had raped Blanche, she had brought on herself, and he could not help himself after months of taunting. Many women would have left Stanley, but it helped to have the handsome looks and strong arms to comfort Stella.
However in the film production in 1951 directed by Elia Kazan, Stella (Kim Hunter) leaves Stanley (Marlon Brando) after her sister, Blanche (Vivien Leigh) is carted off to the looney bin. She runs upstairs to her neighbor's house with her and Stanley's newborn baby. Stanley is left at the bottom of the stairs yelling for Stella. Some say this is a happy ending because the woman had stood up to the handsome brute and left despite the physical attraction because of the abuse and neglect.
In the end, it is all a matter of point of view and what makes a person happy or sad. Many could have never left the young Marlon Brando. But have Stanley played by a man with slightly bad looks who had beat them and cheated on them, then they would have definitely left. So, was the ending happier in the play or the movie? Only you can decide.