How Would Harry Breaking the Unbreakable Vow Have Affected the Piece of Voldemort's Soul?

Question

Based on what we know from canon, how would Harry breaking an Unbreakable Vow have affected him and the piece of Voldemort's soul inside him? What would have happened?

It was determined in Could the Sorting Hat Have Told Dumbledore That Harry Was a Horcrux that Harry is actually not a proper Horcrux:

JKR: "Here is the thing: for convenience, I had Dumbledore say to Harry, "You were the Horcrux he never meant to make," but I think, by definition, a Horcrux has to be made intentionally. So because Voldemort never went through the grotesque process that I imagine creates a Horcrux with Harry, it was just that he had destabilized his soul so much that it split when he was hit by the backfiring curse. And so this part of it flies off, and attaches to the only living thing in the room. A part of it flees in the very-close-to-death limbo state that Voldemort then goes on and exists in. I suppose it's very close to being a Horcrux, but Harry did not become an evil object. He didn't have curses upon him that the other Horcruxes had. He himself was not contaminated by carrying this bit of parasitic soul."

[SNIP]

"I do think that the strict definition of "Horcrux," once I write the [Harry Potter Encyclopedia], will have to be given, and that the definition will be that a receptacle is prepared by Dark Magic to become the receptacle of a fragmented piece of soul, and that that piece of soul was deliberately detached from the master soul to act as a future safeguard, or anchor, to life, and a safeguard against death." J.K. Rowling - Pottercast 12.23.07 - The Leaky Cauldron

So, yes, what would have happened?

Answer 1

I've thought long and hard on this one; these questions that are almost addressed in canon, but not quite, make excellent grey matter fodder. :)

We know from Half Blood Prince that when someone breaks the Unbreakable Vow, that they die. How exactly this takes place, is never directly addressed. It would not be unreasonable to assume that the magical theory behind it is very similar to how Avada Kedavra works, however; I would posit that the Unbreakable Vow is sort of a delayed, conditional Avada Kedavra. We also know from PotterCast Interviews J. K. Rowling, PotterCast #130 that in order to destroy a Horcrux, the container must be destroyed.

SU: So, can I ask this? This is kind of a random question but if Harry had this Horcrux in him, of course, sort of, would he have actually have died, like say when a dragon could've killed him, or when he was falling during Quidditch, or anything?

JKR: Well, you've got to-- if his body had been irreperably destroyed, he has to die to get rid of that piece of soul. His body has got to be irreperably damaged. So a lot of people asked, and I think I've answered this since... but a lot of people immediately said, having finished "Hallows", "(gasps) But then, that means, in Chamber of Secrets when he was pierced by the basilisk..." But no, no, no, no. He didn't die! He didn't die! That was stated right at the beginning with the Horcrux. The receptacle has got to be destroyed. His body wasn't destroyed. He got a bit poisoned, and then he got the antidote immediately. So, you know, that's not gonna drive out this piece of soul. [...]

By now, we all know that Harry wasn't a true Horcrux, but Rowling maintains that the piece of Voldemort's soul within him was there under much the same conditions as a Horcrux. If we operate under the assumption that a magically induced death can indeed sufficiently "destroy the container" of a Horcrux, as in the case of Voldemort using the Killing Curse on Harry, then it is not out of the way to assume that breaking the Unbreakable Vow would have the same effect.

My conclusion, drawn from what we know of Horcrux destruction and the Unbreakable Vow, is that if Harry had broken the Unbreakable Vow, the piece of Voldemort's soul within him would have been destroyed, since it's container would be "irreparably destroyed".

Answer 2

Well, with Harry have a piece of Voldemort's soul, it is "like" he has two souls. There is no canonical writing about whether the Unbreakable Vow's death effect would affect only a single soul or all the souls a person has or whether it can choose which soul it will kill. But, based on what happened in Harry Potter and the Deathly Hallows, where Voldemort use the Avada Kedavra spell on Harry, the piece of Voldemort's soul will die instead of him and Harry will enter a coma state. Since the curse is from outside of Harry's body, this means that the Voldemort's piece of soul is covering Harry's soul, which is why it is Voldemort's soul and not Harry's that is affected by the Avada Kedavra spell.

Now with the Unbreakable Vow, it is not known whether the death effect works from outside like Avada Kedavra or from inside. If it is from inside of soul, then Harry's soul is the one who will die and Voldemort's piece of soul might look for other living object nearby, but if it is from outside (maybe from the bonder?) then Voldemort's piece of soul will die and possibly Harry will enter a coma state just like with the Avada Kedavra spell.

Answer 3

Well, in the Deathly Hallows, Dumbledore says: "'Voldemort himself must so it, Severus. That is essential.'" They are talking, of course, about destroying the piece of Voldemort's soul by Harry's death.

This seems to imply that if Harry was not killed by Voldemort, the fragment would continue to exist. Of course, this doesn't really account for accidents. But maybe the fragment would continue to animate and control Harry's body if his soul were destroyed/killed/detached from the body.

I think that this is the most likely scenario. The Avada Kedavra causes no physical damage- it presumably attacks the soul. The Unbreakable Vow probably works the same way. So the soul would continue to inhabit Harry's body.

Answer 4

Harry as a container would have remained in existence. However his souls would disappear and he would die but his body would remain intact now being fully in control of the horcrux inside of him. Hence vodlemorts horcrux would inhabit Harry and hurry would be no more. Just his shell