I agree with a post on another discussion of this story, which suggests that the final line of the story would make an excellent. Here is how that line might be used as a main title, with an explanatory subtitle:
"'So the storm passed and every one was happy':
The Irony of Adultery in Kate Chopin's 'The Storm'"
Here is a thesis statement that would go with that title:
Although Kate Chopin's story titled "The Storm" is often read as an endorsement, or at least as a sympathetic depiction, of the adulterous affair it describes, a strong case can be made that Chopin implicitly mocks the affair, suggesting that it is rooted in self-interest and deception.
Here is evidence from the end of the story that strongly supports this argument:
Alcée Laballière wrote to his wife, Clarisse, that night. It was a loving letter, full of tender solicitude. He told her not to hurry back, but if she and the babies liked it at Biloxi, to stay a month longer. He was getting on nicely; and though he missed them, he was willing to bear the separation a while longer—realizing that their health and pleasure were the first things to be considered.
As for Clarisse, she was charmed upon receiving her husband's letter. She and the babies were doing well. The society was agreeable; many of her old friends and acquaintances were at the bay. And the first free breath since her marriage seemed to restore the pleasant liberty of her maiden days. Devoted as she was to her husband, their intimate conjugal life was something which she was more than willing to forego for a while.
So the storm passed and every one was happy.
You are correct in suggesting that the plot structure of the story is essential. But the climax of the story is really only important as it allows for the denouement, the resolution of the conflict. Chopin summarizes this so very well in the story's very last line: "So the storm passed and every one was happy."
In my mind, that last line would be a great title for such an essay.
How about this one?
"Kate Chopin uses the torrid affair between Calixta and Alcee to illustrate her belief that passionate love is not synonymous with marriage."