How does Slaughterhouse-Five relate to Sartre's theory of abandonment?

Billy Pilgrim says that free will doesn't exist. The Tralfamadorians confirm this and say that in fact Earth is the only planet they ever visited where such a thing as free will is mentioned. Sartre's determinism is reflected in the behaviour of the tralfamadorians, who only control what they think and not what they do. Vonnegut calls his own attempt in writing the book futile, because it is like trying to stop a glacier.