I'm sure the mirror was put on with mirror mastic. Really gooey stuff. I've never seen if it hardens or not. If it's on drywall, the paper should tear off pretty easily as you pull the mirror. If you are afraid of it shattering, use some masking tape and cover the whole mirror, just get the widest tape you can find, or you may be still taping the mirror when you'r 90! That way if it breaks, it will contain the small pieces. There are sticky plastic sheets that are used on carpet at convention centers, but those are hugh rolls and pretty expensive. Even if you could get some pieces for free, you'd never get it home without it folding on itself and ruining it. Unless you know someone and they have a small piece on a roll left....
But I'm with the others on the mirror in small rooms. Heck, our master bath is long, has a mirror that is 9 or 10 feet long, and 36 to 40" high and I love it! Wouldn't want to take it out. And hope when I get around to doing a bath remodel in there in the future that I don't damage it taking the vanity out. I'm sure it would be too expensive to replace if I broke it.
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At a minimum, I'm Pentatoxic...but most likely, I'm a Pentaholic. There seems to be no known cure. Pentatonix, winners of The Sing Off, season 3