I know GRRM hasn't had any qualms in killing literally any character, but these four... they seem like they have 'too much story' with them. I mean if Arya dies, where does her story go? Nowhere, I mean no one would even miss her, knows she's dead, ect; that'd just be stupid, when she has good potential to affect the main story/other characters. Not saying she couldn't do some epic stuff and then get killed at the end of this season, though. I mean, I ain't going to get to comfortable... still would feel like a waste though.
Sansa, yeah probably safe, I know I didn't like her character in the first season but since then I've liked her, and so much stuff happens in her storyline now that I hope it continues on. If she's killed right now, then what's the point of her surviving the fall, ect. Again though, lots can happen in one season, so who knows. My personal desire is to see her survive though, she's been through so much shit (much like Arya), I want to see them reunite someday at the end or before.
Dany, I would say she's 'too important' to get rid of, sort of like Arya in the sense that if she was killed, what did her story accomplish? Well okay, maybe a few things by now, such as setting a stage in the east for god knows what, and having three dragons loosed in the world... but without her guidance, I feel like the dragons would die off anyway, surely, without ever doing much. Not to mention fans would be pissed if she dies after her story building up so much and then... nothing
She needs to do something huge.
Maybe I just want to see her battling White Walkers with Drogon
Tyrion, hmm... definitely a survivor, I'd think he's got a big chance to making it to the end as well. Also has a lot of stuff surrounding him, all the time. He's very much a center player. However I know how much GRRM likes to subvert tropes and destroy the characters you think are safe, so.... where was I going with this?