no it absolutely doesn't have to
the show writers can make her a dead end if they want to, and they just might.
They don't have to, of course not, nothing's stopping them.
But think of all the time and money that they've invested into her character. That'd be a real waste, especially if there's no growth from just seeing her suffer. Suffer suffer suffer death. Someone's got to approve money for that, and if the point of that was to just prolong suffering, they'd probably tell them to just go ahead and off her if the story isn't going anywhere (or is fulfilled). Which isn't the case for Sansa.
It'd be like killing off Tyrion right now. The show isn't so brutal that it kills off people without having fulfilled some kind of purpose in the narrative. Sansa has yet to fulfill that purpose, as does Tyrion. Or ****, Daenerys. You know Daenerys is going to return to Westeros. Otherwise, why the hell did Martin even bother writing about her, if the story doesn't connect with everything else later. It simply doesn't make narrative sense. Most every other character that has died did have a purpose that was meant to be fulfilled, and was so. There death's, however shocking and unforeseen, made narrative sense. It's why Theon's still alive. He still has a part to play in the story, however small. They aren't keeping characters just to show how terrible their lives are and then offing them without giving a message.
It doesn't make sense within the story to just off Sansa now or keep her perpetually struggling and being humiliated and abused at the hands of a sadist.