I don't know. I imagine it depends a lot on factors mostly to do with how much a jury/judge likes you.

Generally we treat killing others, even if you didn't mean to, very harshly. It's very easy to get incarcerated for a crash caused while driving tipsy, for instance, especially if somebody dies.

I imagine manslaughter is one of those things where you only have to fuck up once, completely by accident, to ruin your life (and a few others' obviously) quite terribly.