Why would Roose Bolton arrange a marriage to Sansa? Easy - it’s his best move to secure the North and it carries very little risk from his perspective. Most importantly, Sansa’s value to the Boltons decreases measurably once she has provided a male heir - preferably, two. After that, she can find her way south to face the King’s Justice, if needs be. But that is by no means certain…
Cersei: Raven says: Deliver Sansa Stark immediately, Warden of the North.
Roose: Raven says: As your Grace Commands. However, the snows have started and it is quite impossible to convey her to you until they end.
later
Cersei: Where’s Roose Bolton and the traitorous bitch!
Qyburn: In Winterfell, Your Grace.
Cersei: We will march an army up there and take her!
Qyburn: North, to Moat Caitlin? No army has ever invaded the North from the South while Moat Caitlin is held. And the Boltons do hold it. Moreover, Your Grace, the Starks happen to be right: Winter IS Coming. It’s coming now, in fact. The Citadel reports the snows have started north of the Neck and are falling now in the Riverlands already. We can’t march North to lay siege to Winterfell during Winter. Not until Spring. May the Seven send that the Winter lasts only a few years. Though a long summer does point to a long winter. A very long winter, perhaps…
Cersei: Damn that Roose Bolton! I’ll flay him alive. When the snows melt, I’ll kill him!
Qyburn: No doubt your Grace. Of course, by the time the Winter ends, Sansa may well have given birth to as many Stark-Boltons as Roose Bolton is likely to need. You may find he’ll just put her on a ship at Whiteharbour and send her to King’s Landing trussed up like a Goose when the winter storms abate and the ships return to the Narrow Sea. Wars are expensive and Roose Bolton will have no further need of her after the Winter, Your Grace. And Roose Bolton does count his coppers meanly.
Cersei: glares. We’ll see.
Qyburn: One thing is for certain Your Grace. Now that winter has arrived, Sansa Bolton is not going anywhere.
meanwhile
Ramsay: Father, the Maester says a Raven came last night.
Roose: One did. From King’s Landing. The Queen Regent wants your bride’s head on a spike.
Ramsay: She’s mine now Father.
Roose: She is, for now. And after the Winter, once she’s whelped a brood of Stark-Boltons by the end of that, we’ll see. If King’s Landing still wants Sansa, we may have to let them have her.
Ramsay: Father, that would go against our traditions. What would our people think of that?
Roose: Quite poorly, I’m sure. We’ll have to arrange for the Lannisters to kidnap her at sword point so we can blame them for it. If it comes to it, that is. But after this winter, once thing is for certain: Cersei will no longer be Regent.
Ramsay: Are you sure …
Roose: Oh yes, quite sure. Our Good King Tommen will be many years older by then, and come what may, he will be much too old for a Regent. There will be a new Hand along with this new King. And the Queen will not want the Queen Mother in King’s Landing, you can be sure of that, too. The bankers tell me the Lannisters are short of gold and this winter, food will be more important than gold – and the Tyrells have all the food. And soon enough, all the gold too by winter’s end. I’m told Queen Margaery is a good friend of your lady wife and does not believe her guilty of poisoning Joffrey. Lord Baelish tells me Margaery blames the Imp, but not Sansa. We may find that come spring, Sansa’s head is no longer required. And if she is still required for the headsman in King’s Landing, well, being a widower will provide you with new opportunities here in the North. We’ll have Sansa’s children by then and that is what our people require most. Now run along and see that you put a new Bolton son in her belly this evening.
Ramsay: smiles