User blog comment:FairyRaven/Fairy Tail Chapter 416: Tartarus Arc: Final Part, Review and Commentary/@comment-77.194.131.213-20150119141826/@comment-7418318-20150119144031

It'd be interesting if they had to make a tade with Franmalth. They let him go free and in return he sucks the Demonic parts out of Minerva, turning her into a pure Human again.

For Franmalth this deal is perfect, since he survived, regains some strength and is allowed to go. And obviously it's also a good thing for Minerva.