Harry doesn't show up for his first day at the Auror Academy. But... well it's not like too much can come of that right?

With a fantasy world there are always plenty of changes that can be made from small to massive. It could be something as simple as a talking hat saying a different nonsense word, to all of Earth being destroyed and wizards relocating to the moon. In this case though, what would happen if an only child got a sibling? In this case: Nympha-don't-call-me-that Tonks.