Well, it wasn't my original intention to off the entire family. And I did save my game before going in. But it seems it got overwritten after the fact.
On the plus side, I already finished the questline from my oligarch, and the family I whacked was not his. But killing without good reason (such as my own safety and/or significant profit) really isn't my character's style.
Seeing as I didn't get anything significant (other than satisfying my curiosity), I'll probably go back to the older save, even if it means it'll take me an extra hour or so to catch up to where I was before my home invasion. I mean, yeah, my character kinda doesn't like the whole oligarchy setup, but if breaking it up a bit won't change anything, then I as a player feel like "why bother."