Prez knew what was going on, on some level, that's definitely why he gave Aoi that charm that will protect her. Everyone's talking about their ship sinking but I don't think so. This may have been something Hanako planned, or simply allowed to happen because it suited his overall goals, but I don't think this is as black and white as the author is portraying here.
My money is on Aoi being able to return in some form.