I think the Night King will be successful in his mission at Winterfell, meaning that Bran will die. And therefore Theon, as Bran's protector, will die as well. And it's just as well - that brings Theon's arc to conclusion, both punishing him and redeeming him for his betrayal of the Starks. As for Bran - as the reviews point out, he tells people he's the three-eyed raven more than a vegetarian announces they're a vegetarian. He's in danger of being a caricature, so he really should die for the good of the plot.
To get access to Bran, it's likely that those on the front line will all fall. Brienne, Tormund, Podrick and Grey Worm in particular will die. Probably Edd. Maybe Jorah, maybe Gendry. I hope Arya and Sansa survive, but since this will probably be the last time we see Winterfell, all bets are off for anyone who is traditionally headquartered there. I think Jamie will be the big death for next week's episode. He and Brienne got the most attention recently, which is a bad sign for them.
As soon as Bran is dead, either the living survivors retreat South, or the army of the dead wheels around, ignoring the others at Winterfell, and heads for Kings Landing. Either that or we have a final defeat of the Night King. I sure hope not. I'd hate to have the Big Bad of the whole series defeated in a single episode. I'm going to stand by the theory that the Night King isn't at the Winterfell battle at all, but instead is flying to Kings Landing to make a million soldiers. They seem to be setting up for a three-way dragon battle, now that Dany and Jon may be turning against each other.
No idea what happens to Sam and Gilly. That's the least of my concerns. Other than Tyrion, I think everyone in the crypts is expendable to the plot at this point, including Varys and Missandei. It's likely that Tyrion disobeys the order to be in the crypts and they all get wiped out by a fireball or something.
The only guaranteed survivors of the battle at Winterfell are Jon, Dany, Tyrion and Sandor. Jon and Dany for obvious reasons. Tyrion to kill Cersei (in accordance with the prophecy). Tyrion also has to have a reckoning with Ser Bronn of the Blackwater. And of course, Sandor has to be there for Clegane Bowl.
Which of the major characters AREN'T at Winterfell? Is it just Cersei, the Mountain, Qyburn, Euron and Melissandre? Have we heard the last of Yara? If the dead end up swarming Westeros, it may be up to the Greyjoys to evacuate the living. So Pyke, Bear Island (home of the Mormonts) may come back into play.