I do not know if this has been discussed before (if so someone kindly redirect me to a similar post), but I'm a new reader and I love what if's.
So for the sake of this post let's assume Tywin leaves Harrenhal in ACOK, Edmure doesn't offer him battle and Robb does indeed manage to annihilate his army and capture him.
What then? Do the Tyrrels fall back to Highharden after failing to link up with Tywin or do they continue marching to KL and save it anyway? And if so what happens most likely after that and how would the story probably change? Does Robb's ass get saved by that?