I would love for this to happen, and I will be cheering if it does. BUT I also wanted a Stark to kill Joffrey, and that didn't happen. For all his sins, Joff got off too easy IMO, and sadly, no one truly got vengence. Joff was killed only to set up Tyrion and free Margarey. With Martin, you never know. Old age could kill the Late Lord Frey (or he could outlive them all).