How could I give a twist to the story "The Last Leaf" by O. Henry and change the climax?

The climax of the actual O. Henry story is that Johnsy survives having pneumonia and Behrman dies after painting a leaf on the wall so that Johnsy doesn't see the last leaf fall. If you want to change the climax, you can change either part of the resolution of the story. For example, Johnsy can sadly die after she sees the last leaf fall from the wall. Another ending might involve Behrman surviving instead of perishing from pneumonia. A third potential ending might involve Johnsy surviving and Behrman surviving as well. If you wanted to add a twist to the story, Behrman could become a well-known painter after news of his painting the leaf on the wall begins to spread. People could arrive from miles around to see his masterpiece, and he could achieve the fame and renown he has long sought but has not to date achieved.