The shit is really hitting the fan, finally. I mean, there is 5h of Lost left, they have to kill some of the main characters.. I'm actually glad Sayid died like that, in a heroic manner. It was redemption for him. So yeah, bye bye Sun Jin and Sayid, you will be missed.
As for Frank, part of me is holding out hope that he somehow survives.
After all, we didn't see any evidence of him dying - just getting
knocked out and going under water. Who's to say that he didn't wake up
and swim out? I have to think that the writers would have given us at
least a brief shot of his dead body in the submarine if he actually died
- his character deserves more than an off-camera death, doesn't he?
Yep, I'm sad that Frank is gone - but would probably bet money that he's
not actually dead.
I think the only character that is safe and won't die is Hurley.. I'm not sure he'll become the new Jacob, Jack seems to be the favorite for that post but Hurley is just the soul of Lost and I'll bet my life he will survive.
Kate? She's already dead. There is NO CHANCE she'll survive. She's not even a candidate anymore. Before coming back to the Island, she already gave Aaron away, so there’s no way that she
could reclaim him upon return from the Island.
She’s already attempted a relationship with Jack that failed. What else
does she have in life? Yep she's dead.
Desmond, despite being my favorite lost character, will obviously die saving the survivors, and the world. A sacrifice for the good cause as Widmore told him before. Might be one of the very last scenes.
Sawyer ? bah 50/50 for him.. If he dies, it sure will be with a last "son of a bitch" hurrah

!
in the end, I see Jack being the new Jacob and Hurley surviving with a few others.