Question

I am in the process of having the bathroom tile replaced in my bath/shower. I have one (major?) concern. When the new guy ripped off the old tiles last week it left a five inch section of standard sheetrock on the right-hand side at the back of the tub from floor to ceiling torn up with many soft spots and gypsum falling out. I am under the impression that when he returns to install the new tile (it is actually a floor tile we are installing on the walls, so it is heavy) that he is going to install cement backer board where it was originally and then just cement over the damaged sheetrock in this approximately five inch wide area that extends from floor to ceiling on the right-hand side of the back of the tub. I think he said he has to do this because there is no 2x4 behind the sheet rock if he cuts it out. I want this installation to last another 20 years. I am very naïve about these remodeling things. What is the correct course of action?