How did things stand between Roose and Tywin before the Purple Wedding? Roose knows that Tywin has Sansa–does he expect all along that Sansa’s descendants, not his own, will rule the north? Does either man expect their deal to last?

Oh, they were both planning to betray one another: Tywin was going to use Roose to take out the Ironborn and the wildling threat and weaken him in the process so he couldn’t threaten Tyrion and Sansa’s claim to Winterfell, Roose knew that once he was in the North, he could act with a free hand no matter what King’s Landing said.