Regarding Wyll's pact with Mizora:
Mizora's basically portayed as an evil lawyer type. Because it's not an actual heart, it does not count as one for the clause. Law is brutal like that. She won't be letting him off on a technicality here, however you do get that opportunity later with the rescue mission. Whether or not Mizora would be up for a buyout is a different story and would be a fun way to give secondary use to the Soul Coins other than simply selling them, but it would also take away from Wyll's character development.
