I think Stoneheart has some plans for Jaime besides just killing him. She's probably still torn up about RW and wants to kill more Freys. She might use him to get the BWB into the Twins and take control of it from the inside since they don't have the manpower to take it but they have the power to hold it. Once they have the Twins, the riverland Freys will be pretty much extinct while the northern ones are getting slaughtered courtesy of Stannis and Manderly. Once the RW has been avenged Stoneheart will probably lose the gift from R'hllor and Gendry might take up the leadership of the BWB
