Not marry, but Jon Arryn would probably at least try to betroth him with Arianne Martell as a way to make peace with them. Robert didn't care for marriage and could wait even a decade, spending it with other women. Doran may even agree under condition she doesn't go to King's Landing before she's of age and ready to carry their vengeance. Other changes, if Jaime declined to leave the Kingsguard, which could change with his sister not present, I suspect Tywin himself would consider marrying again. With no ties to the Iron Throne, he needs allies and a heir that's not Tyrion. Even with these changes the war would happen, if only because there were too many people who wanted it to happen for their own gain.