Payback on unbreakable vows

[lazyvix3n]

No: HPFGUIDX 135259

Is it possible that what determines the outcome of an unbreakable vow
isn't just circumstance, i.e. Suppose that, as happened, Malfoy had
not completed the deed and Snape and not completed it for him at that
particular moment in time, would that mean he had broken his vow? and  
would it automatically mean death? Maybe the Vow maker has to do
something that means he totally cannot fulfill the vow. Like kill
Draco, or help Dumbledore emigrate to Iceland.
It may even be down to the person that the Vow was made to to invoke
the punishment. Maybe via some wizarding court such as the Wizengamot.

I guess we've all trusted Wise old Ron Weasley's take on the finer
points of advanced magic.

Where did I put that book on Wizarding Law???

Mandy