There's a poster here named 1buckie. Has an incredible collection of vintage Weber kettles and cooked pretty much everything on them. A grilling/BBQ sage, IMO. One of my favorite posters but according to the membership list has not posted here in over a year.
Posted a thread few years back asking how to collect BBQ drippings for gravy. Dumbass that I was, had always just put a pan under the meat and the drippings would burn up in the pan. 1buckie answered with pictures of how to do it...a pan filled with water and covered by heavy duty foil in sort of a reverse tent.
My point is, if doing the rib roast whole, catch the drippings. Au jus, gravy, add it to sauteed mushrooms, etc.
Hope 1buckie is still around and just on an extended hiatus.