Dan, I believe that I would get some drywall of the same thickness and replace a section 16" wide by about 12" high centered over the new hole. This will let you run new drywall screws into the studs on both sides of the hole. Put some drywall compound on the top and botton of the new section so that is also locked into the old wall. After you fill with compound, sand flush, prime and paint, you can install new molly bolts.
You could run some thin wood slats into the hole and fill the hole, but the fact that you have had a problem once means that you might have a bigger problem if more bracing came out with the mollys.