Spoilers ahead...

So my Nord assassin Eydis dutifully killed Vittoria Vici as part of "Bound Until Death"; unfortunately pandemonium broke out when the bride took an arrow to the face.

I quaffed an Invisibility Potion and dashed off into the night, but an old lady wouldn't stop following me, and throwing Frost at my backside. I killed her, but then Vittoria's father in law (Vulwulf Snow-Shod) and the husband to be (Asgeir Snow-Shod) showed up and took a couple swings, so I killed them too. And then the Penitus Oculatus agent and two Solitude guardsmen showed up, so I was obligated to slay them as well.

When it was all said and done, there were no more witnesses (dead men tell no tales!), so I went to claim my reward. However, I don't want to miss out on any potential quests involving the two Snow-Shods, or the old lady. Will I lose out on a quest or two, or can I go ahead and continue along with my current save?

The only guest that offers a quest who is present at the wedding is Noster Eagle-Eye; the beggar. It's a minor, radiant quest so if he is killed, the game does not inform you that you have failed that quest.
In any mission or events, when you kill an NPC that is part of a secondary quest, a message will show saying you failed that NPC's associated quest. It does not show for misc. quests.

And a job well done on the wedding. The more blood and corpses the better I say.

Heh I did it exactly opposite. I hid, dropped a gargoyle on her head a la Baenlin, and then stayed hiding until the red dots went away. Then I looted her corpse, saved, cannibalized her for teh lulz, then reloaded the save. Then I ran across my Argonian friend who decided it would be a great idea to kill a Pen Oc dude, so I watched them duke it out and then collected my new Pen Oc armor. Came in handy (for a RP perspective) when I had to visit the Pen Oc outpost.