House Whent fanfic
I have a fic in mind featuring the heir to Harrenhall (an OC grandson of Shella Whent) during the War of the Fallen Kingdom, and I have two deviations from canon in mind:
The OC marries Jeyne Westerling instead of Robb, so, not Red Wedding. But I wouldn't know how to develop the story after that.
Robb still marries Jeyne, but the OC is saved from the Red Wedding by returning to Harrenhall when it's under Roose Bolton's control. There, he resists the Lannisters there. In the end he would surrender with the rest of the Riverlords, but I don't know what conditions the Lannisters would give him.