Assuming there are no more Boltons in direct succession, (which is a reasonable assumption given that prior to Fat Walda's baby, Roose was desperate enough to engage in the relatively unusual act of legitimizing a grown bastard with little knowledge or training, who he noted had behaved in a personally embarrassing manner to him more than once), ie no brothers, no living fathers, uncles, etc, it would then fall to any cadet branches of the Boltons. They would look for any cousins, distant or otherwise who still held the Bolton name. Then assuming, there are no cadet Boltons, you would run into a stickier situation because you would started looking at Bolton women of the past would have married into other households and who would have been their heirs. It's all in the game. That's one of the ways that suddenly you thought a holding that was firmly in the hands of your dynasty suddenly falls into possession of another House. But no, Sansa doesn't have any claim to the Dreadfort simply because she was married to Ramsay, any more than she has a claim to any Lannister holdings by virtue of being married to Tyrion. The notion of the spouse inheriting anything is pretty much a modern conceit. Primogeniture laws will pretty much look to maintaining the family legacy over everything else.
The title of Lord or Lady Paramount would fall to the king or queen on the iron throne to bestow. Sansa would not really have any claim to it, because the last legitimate holder of the title was Roose Bolton, not Ramsay Bolton. I am pretty sure that, at the very least, once Ramsay married Sansa, who is regarded as a criminal wanted for regicide, Tommen's advisors would have told him to consider Ramsay Bolton to be in rebellion, so it is highly doubtful that the title of Lord Paramount of the North fell to him. He might have been regarded as King of the North if enough bannerman rose if and when the crown came to arrest him, because that title is not dependent on the sufferance of monarch on the iron throne like Lord Paramount, the but I don't think he ever claimed either of the two titles, just Winterfell.