I never read the 'Game of Thrones' books, but, like much of America, I have become enthralled in the story as it's unfolded on HBO. I love epics. I love soap operas. (Don't make that face. So do you. The only reason people don't watch 'Guiding Light' or whatever the hell is because it airs daily and has been on for fifty years, making its story lines impenetrable and insane. See also: superhero comics.)
So I am relatively unspoil't (some might say Unsullied, but that would take balls) with regards to how this whole thing will shake out. That won't stop me from positing, based largely on the mechanics of How Epics Work (which is one of the main reasons I like them; they're the stories that are least apologetic about letting you see how the gears work) whose survival is likely through this season of the program and beyond.
Similarly, Sam, Theon and Bran are safe for now (as is Bran's running crew), given that their plot lines don't intersect with anything in a dramatically meaningful way. Implicit in this is the lesson that if you want to survive in Westeros, get the fuck away from everything and everyone even remotely interesting.
Nothing bad is going to happen to Joffrey Baratheon. He's too much of a shit and we all hate him too much for any misfortune to befall him. Sansa, in the obverse, is safe. As long as she can suffer, she's going to live a long life. The Red Woman will keep around, because the night is dark and full of terrors, y'all, and because she's the most recognizable prophet of her religion.
Jon Snow is probably okay, at least through this season, and I wouldn't count him out as a major point-of-view character. He is the lens through which we view the wildlings and while it's concievable Sam or Ygritte could follow on in his stead, it seems unlikely. Arya and the Hound probably sit around here. I can see Arya lasting the whole series, but that's just because she's awesome, nothing to do with the mechanics of the story.
Both due to their knack as survivors, character-wise, and their ability to fit in just about any story, both Varys and Littlefinger are safe for now, but I wouldn't be surprised if one of them snuffed it long before book seven. The other ends up as the Hand, for about an hour.
I don't have a lot of hope for Robb, That Lady Robb Married, or Cat. Or the Blackfish. Or Cat's Idiot Brother. There are just too many people knocking about Riverrun or the Twins or wherever the hell they are right now. As a head of state, Robb is nominally protected, but we all know the North is going to get it in the kiester before all this is over.
Similarly, King's Landing is just chock full of disposable characters. Somebody in the Lannister clan has to bite it, and I would wager Cersei or Tywin (the latter gettting it from Joff, the former, I dunno, falls down some stairs?) ahead of Tyrion in the death department. I think the diminuitive Lannister will survive at least through this season and in to the next. Bronn? Shae? Their days have to be numbered.
The buddy-cop movie that is Jamie and Brienne will last at least until this season, long enough (I think) for one of the two of them to snuff it. Probably Brienne as it would hurt Jamie, and the only thing more integral to your survival to the Game of Thrones plot than your (eventual) plot utility is your capacity for suffering.
Stannis? Dead. Davos might live but he's like Mormont: without his liege to back he doesn't really serve a purpose, and Stannis might well outlive him, but I wouldn't wager for long. Gendry is similarly ready for the noose. He could outlive Stannis if the Red Lady sees him as a more legitimate line to power.
Probably the one guy with the best chance of living through this whole thing is What's-His-Name-That-Keeps-Coming-Back-from-the-Dead, but since I forgot about him until now, odds don't look too good.
However, it's possible the whole tenor of this story could change. The Red God went from unmentioned in Season 1 to enabling shadow demons and multiple resurrections. The whole war of succession can't last the entirety of the series. The Ice Zombies are coming and they're gonna wreck the North, and it's possible that the show will shift focus to whatever power is behind the Red God, whose disciples I've personally taken to calling Cylons.
Who'd I miss? If I missed them, they're probably dead.