Spoiler: Warning: Spoiler! I don't even think Walder makes it that far. They've proven that they can't be trusted, and they've made some enemies you don't want to fuck with. If Tywin was still alive I know he would take him out. The chaotic situation that the Lannisters and the Crown are in might be the only thing keeping Frey alive right now. Manderly and Lady Stoneheart are slowly eating away at his forces. If Stannis ever makes it that far he will feed the lot of them to the fire. Walder fucked up. GRRM doesn't do happy endings, but he does do retribution. The one guy that I could see not getting his in the end is Littlefinger, simply because he has nothing to trip him up. He has no pride in his family or homeland, no honor or dignity or morals. He's an organized sociopath, and now he's in line to rule the Riverlands, is in control of the Vale, and has plans to take the North. If he can find a way to command loyalty from families that are older and more powerful than his (which will be difficult to be sure, but I'm sure he has a plan), then he has a lot to bargain with anyone. OTOH, I have a suspicion Sansa might kill him.