On mine, the area in question was across the end of the bathroom, under the window, beside the john, and extending from the tub surround to the far wall - almost exactly 4X8 feet. When the girls were small they hung on the towel bar to look out the window and pulled it out. When redoing the bathroom removing that section of damaged drywall and cutting back the required studs with a router is not an onerous job, and you only need sheathing grade, not even G1S.