There's no easy way I know of.
You need to break it off.
First apply duct tape in squares that so many pieces will not fly everywhere. And wear gloves and glasses.
there are many practices.. but sadly, if you are trying to save it for reuse? its risky because there is no telling how much glue the installer used to put it up!
What's more important to you, the mirror or the sheetrock. You will pretty much have to sacrifice one or the other.
You could try removing it with the type of wire they use in auto body shops to take out windshields.
Otherwise, your best bet might be cutting away the sheetrock, but that's not too hard or expensive to replace.
I have heard of some folks using a thin wire behind the glass to separate the two....follow the same safety procedures.
Score tightly around the mirror with a sharp utility knife- press lightly - just enough force to cut through the paper and not all the way through the wall board- then pry up the mirror. If you are going to replace the mirror - get a bigger one to cover the mess. :)
good luck impossible
I wallpapered over ours!!
Hopefully you have a FRIEND that has some "glass suction cups"....I did the same thing in two of our bathrooms...I tried the "wire" process, I even bought some handles that "secure" the wire when TRYING to shimmy back and forth behind the mirror....the handles broke!! My wires sat there for a couple of months, but I kept trying!! Finally my niece has a boyfriend that had those suction cups....I am sure you have seen them....they can be used to CARRY large pieces of glass, or even marble!!! The down side is that they are VERY expensive!!!!! MAYBE???? (just thought of this) you can rent a pair from the big box stores?? Mine came off in 2 minutes!! One broke, the smallest one...and the large one did not!! It took all of two minutes to get them BOTH off!! GOOD LUCK!!!! Hopefully you can rent them????
I removed a large bathroom mirror glued to the wall before. What I did was squeeze goo gone (copious amounts) at the top to run down the back of the mirror. Then I used twine starting at the top and kept working it side to side towards the bottom. It was like flossing. It took some time but the mirror popped off the wall eventually. My advice is to have another person with you. I was alone and incredible lucky that when the mirror fell forward off the wall it didn't shatter or hurt me.