First, I'd like to mention that I don't read any forums or any other fan sites, rumor sites etc... related to television show. My theories are based purely on the content presented in the weekly TV episodes. By the way, if you have no interest in the show, you should probably stop reading now. For the rest of you, if you'll allow me to indulge myself...
To start, I'm going to define some of my terminology. At the end of last season, a nuclear bomb was set off... I think... and as a result of that, the Lost universe was split into two timelines. I'm going to call one timeline the "
Never-Crashed Timeline." This is the timeline that takes place mostly in Los Angeles with Sawyer as a cop, Ben as a teacher, Jack as a dad etc... I'm going the call the other timeline the "
Still-Crashed Timeline." This one mostly takes place on The Island with Juliet dead, almost everyone else dead, the blown-up submarine etc...
Also, I'm going call the smoke monster that has taken the form of John Locke "
Monster-Locke." it's an nasty name, but considering his activities so far, he kind of deserves it.
So onto my predictions:
#1 Everyone is going to get off the Island alive.
From what we've seen in the Never-Crashed Timeline, nearly everyone is still alive. Definitely, everyone from Flight 815 is alive. Also through Desmond, characters in the Never-Crashed Timeline are starting to remember their lives from the Still-Crashed Timeline. In fact, at the end of the most recent episode, we saw a Never-Crashed Hurley with what appeared to be complete, lucid memories of his Still-Crashed life. This is how everyone survives. When the series is over, all the main characters in the Never-Crashed Timeline will have complete memories of their Still-Crashed life, and they will be alive and well in LA. In a sense, detonating the bomb succeeded. It created the new Never-Crashed timeline and allowed everyone to live... and because of Desmond they will all remember life on the Island. (Their Still-Crashed counterpart will likely die on the Island)
#2 ...except Jack.
Still-Crashed Jack will be the last remaining survivor on the Island. The series will end with him and Monster-Locke sitting on the beach in the Still-Crashed timeline. Both of them will never age. Jack will have the job of forever be trying to stop Monster-Locke from leaving and the two will forever be debating... kind of like the way we say Jacob and the monster at the end of last season. Secondary to this, Jack in the Never-Crashed Timeline will likely die. By the series end, there will be only one living version of each character. For Jack, that will be his Still-Crashed life. For everyone else, it will be their Never-Crashed life.
Personally, I think that sounds reasonable and it would create a very satisfying end to the series. I'm looking forward to seeing how right/wrong I am this Sunday, and I bet I'll still be surprised at what the television series will pull off.