I think G.R.R. just wanted to shock his viwers/readers. There was so much more he could have done with this characters but just like with Ned, he threw the white flag.
I am guessing now, based on the movie episodes: with out the Wolfs the conflict is pretty much gone now, right? Who is going to fight Lannisters?
Stannis is still out there. The alliance with the Tyrells is shaky. Dany has dragons and an army. The Others (White Walkers) are coming, eventually. The Brotherhood Without Banners is still on the loose. And of course, not all the Stark bannermen pulled a Roose Bolton and switched sides. The North remembers...
Stannis lost his battle already in Season 2. So he is out of the game for now.
Dany is also out of the game, her 3 trump cards are still too young.
The Brootherhood is just a small band of bandits, they aren't really in the game.
So who is still playing the game?