What is the climax of "The Secret Life of Walter Mitty?"

You could argue that there is no real climax in this story
as Mitty does not ever change or reach a turning point. For argument's sake, you could
analyze his final daydream. He envisions facing a firing squad as a form of suicide. Is
he metaphorically killing his former self in order to become more assertive and stand up
to his wife (or act more responsibly so his wife won't nag him so much)? Or does he
really dream of dying as a form of escape? In reality, his limited options include
standing up to his wife, positively changing his behavior, and/or leaving his wife. He
could also kill himself or kill his wife. But considering that over the course of the
story he his weak and passive, it's unlikely that he suddenly decides to make a
significant change and much more likely that he simply continues to be a doormat to his
wife and the firing squad is just the next daydream and many more will
follow.