In addition, I'm going to assume that the Red Wedding is avoided somehow, and that the Frey's remain on Robb's side. But I will allow that Tywin still gets assasinated and Cersei takes over. I don't think ti matters one way or the other. Yes, it would be a blow to the Iron Throne, and would be a good bargainng chip for forcing them to let the North go. But I think even if that happened, the Lannister/Tyrell/Crown forces (which I will simply call "the Crown forces") would not accept a peace, and would march their 80k+ men west (probably with Jaime as commander) and either meet Robb's forces (which altogether is maybe 25k) in the field, or start sieging his holdings if he retreats. If they siege his holdings, I don't think it matters if he holds Casterly Rock or not., as in order to enforce their claims (over the Riverlands and the North) the Crown will really have to retake Riverrun, Winterfell, The Twins, etc. Forcing them to retake Casterly Rock would just delay them and/or split off a small number of their forces (enough to maintain a siege against Casterly Rock) On one hand, I could see the Crown forces simply failing to achieve their objective of reconquering the Riverlands/North, as they will have a tough time to do so before winter comes and it will be unfamiliar territory. On the other hand, I could see them winning a war of attrition. Particularly because Robb will have to drive the Ironborn out of the North, and will inevitably lose men and resources in the process. So taking Casterly Rock, probalby gains Robb very little. Yes there is loot there, but probably not enough to affect the outcome.
JC Denton replied to Good Guy Garlan's topic in General (ASoIaF)Brienne: Either serious abridge or completely omit Brienne's POV. The problem is that we, the readers, already know she is doomed to fail her quest. Yes there is the really remote possibility she gets to the Eyrie (I think she mentions that might be a logical place to look), but is anyone believing that is she is going to somehow outwit Baelish and get Sansa? Cersei: Ditch the Maggy the Frog prophecies (one too many prophecies) and the whole shiving her childhood friend nonsense. One of the great things about the series was the depth of the characters. at least the ones that had PoVs at least. Cersei was a huge disappointment to that end. If Martin is going to insist on making her Joffrey v2, don't give her a PoV.