When you are done tearing up the wall, you will need to skim coat it with drywall mud then prime before you put any paint or new wallpaper up. If you do the whole wall it will look best but you might get away with spot repairs.
Leave what you can of the drywall paper in place, sand the ugliest spots before skim coating. If you pull it off, the gypsum will crumble and make a real mess.