Regardless of the reason for doing it, killing the dog in the story feels like a cheap emotional ploy. I think it's a common trap for new writers to fall into because we learn pretty quickly that "happy" stories are boring and even a little juvenile. Killing the dog is an easy way to impose grief on a reader because virtually everyone likes dogs.
Sunday Photo Fiction: The River
My brother and I grew up in the river. Like tadpoles or insect larvae, we spent our youth maturing in the fetid water. We collected things that floated and things that sank. We collected bottle caps, rubber tires, shiny glass, and rusty old cans. We collected scabs and rashes more than once, and we cleaned each other’s wounds.