My guess is that using a fantasia flips an "off" flag to "on" on your character, meaning it's something specifically saved to your character when you log out, meaning it *should* be safe from maintenances, even big ones like 3.0.

My second guess is that there are a lot of people who are going to be doing this and that there will be a big revolt and reimbursements having to be made if it *doesn't* work this way.