Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Muriel and the three other adult women in the story are painted in a most unflattering light, bordering on a caricature (all they talk about is fashion, even while dismissing the importance of Seymour's mental illness). Their world, priorities, and actions are judged and condemned as materialistic and shallow. As far as Seymour's death is concerned, the authorial tone maintains its distance from the topic at hand, betraying no real opinion of its own on the matter. The author leaves it up to his reader to interpret this tale.