Replacing it is more or less impossible, so that's out of the question. First you should download an app to check what sensors still work, if the compass and accelerometers are also dead, you are probably screwed as the IC may have fallen off. Only way to do it in this case would be through warranty and pretend you don't know anything about dropping it. If it's only the gyro though; A gyro sensor is partially mechanical, on a micron scale so there's a possibility one of its little arms have stuck to the edge of the IC. There is a small chance you could get it to work again by tapping the phones edge against a hard surfare, could try on the opposite side of where it crashed into the floor if you can figure out what side that was. Worked on my old XT720.