When you lost the outer skin of drywall, in most cases you lost the adherance part of the wall. In other words nothing will now stick.
Try getting some joint compound and lightly floating a thin layer over the area. Let it dry for 24 hrs, then lightly sand, then apply another thin coat, then let it dry. Then do this again with another light coat.
If this stays, then lightlys sand it down and do your texturing, then do your priming, then paint it.
Some may say that use interior spackling in lieu of the compound. Just see which one works for you.