The quest would simply not begin for me. Susanna would never leave the Candlehearth, thus Calixto would never kill her.
If you don't care about the immediate beginning of the story of the quest - you can skip straight to Step 9 and forgo finding Susanna's body, and talking to the guards.
If you pickpocket the key to Hjerim off of Tova Shatter-Shield, and enter Hjerim, the quest will begin and jump straight to "Follow up on the evidence from Hjerim." as soon as you pick up one of the "Beware the Butcher!" fliers.
You can then go through Hjerim, find all of the evidence, and continue the quest normally.
If you're like me, and enjoy keeping as many active NPCs in your game as possible (Makes the world seem more populated.), you can skip the 3-day waiting period and not have another npc killed by Calixto. Once you have the amulet identified, sell it to Calixto, then go straight to Wuunferth. Do not speak with Jorlief. Wuunferth will tell you where Calixto will strike next, and if you're fast enough - you can save his last victim before he kills her.
This method gets me a completed quest, Hjerim, and peace of mind everytime. All though Susanna's corpse will still appear in the graveyard. Poor gal.
Hope this helps someone! =)

She's been dead on the grave on both of my characters.
