False.
In James Thurber's short story "The Secret Life of Walter Mitty", Walter never abandons his world of fantasy and adventures.
Throughout the story, he has different daydreams in which he is an important person, such a surgeon or a patriot sacrificing his life. And at the end of the story, when Mitty is waiting outside a drugstore for his wife to run an errand, he starts fantasizing again about, this time about facing off against a firing squad.