Let me begin by clarifying a point that's crucial to my claim. I believe that detonation of the Jughead's core creates an "alternate" reality. The catch is that this alternate reality is the timeline of events depicted in Seasons 1-5. Everything we've seen assumes that our Losties crash, travel back in time, and detonate the bomb, which causes the Swan protocol, which causes the crash. Miles was 100% correct that our Losties were always the cause of the Incident -- in the alternate reality.
The "primary" reality is one in which Oceanic 815 lands safely at LAX, so our Losties never travel back in time, and the bomb is never a factor. Jacob is a fourth-dimensional being capable of transcending time and space. Dr. Michio Kaku notes that such a 4D being would be omniscient and omnipotent in three dimensions, just as a 3D being is god-like in 2D Flatland. Jacob uses this power to manipulate the primary timeline, creating the alternate reality in which our Losties cause the Incident.
That brings me back to Juliet's choice. At the end of Season 5, she's frantically hammering on the bomb in hopes of detonating it before the Swan anomaly reaches critical. We see a white flash like we did when Desmond activated the Fail-Safe, a similarity that's no coincidence. I believe Juliet's consciousness will be blasted across spacetime like Desmond's. Juliet, however, will be hurtled into the primary reality, where she will meet Jacob. Here's how I imagine their encounter:
Juliet: Everything's been reset...Daniel's plan worked!
Jacob: No, Juliet, this is what reality looks like if the bomb doesn't detonate.
Juliet: I...don't understand. I remember setting off the bomb.
Jacob: I'm afraid it's not that simple. Right now, there are two possible futures superimposed like Schroedinger's cat. There's the one you remember, which actually depends on the bomb exploding. And there's this one, in which the bomb fails to explode, so Oceanic 815 never crashes. You have to decide which future happens.
Juliet: Why would I choose a future in which I'm dead and the plane still crashes?
Jacob: We all make sacrifices, Juliet. Before you decide, I have something to show you...
He will take her on a tour of our Losties' lives in the primary reality. Judging by the Comic-Con videos, aspects of this reality are familiar. Kate is wanted for murder, and Hurley still the owner of Mr. Clucks. Certain things remain the same because they're not the product of Jacob's intervention, but rather what fate intended. I'm guessing Juliet's sister Rachel dies from cancer in the primary reality -- assuming Ben didn't lie about Jacob healing her. Juliet may still be married to that awful Edmund Burke.
This tour will culminate in Juliet's encounter with her beloved Sawyer. She will be dismayed to find he's the pathetic con man of his flashbacks in the primary reality, a pale shadow of the LaFleur she loved so fiercely. Juliet will realize that, for all the grief the Island has caused them, it also has been a positive force in all of their lives, including her own. Like Charlie, she will choose to sacrifice herself, detonating the bomb and preserving the temporal loop in which our Losties cause the Incident.
If this seems familiar, it probably is. In Frank Capra's classic, It's a Wonderful Life, beleaguered George Bailey wishes he'd never been born. His wish is granted by guardian angel Clarence, who shows George how his hometown would look if he'd never existed. George is shocked and saddened by the changes, particularly in his wife, who is now a lonely spinster. Realizing that, despite his troubles, the world is a better place because of him, George begs Clarence to restore the reality he remembers.
In the end, George returns to his family, and Clarence gets his wings. No similar such happy endings await Juliet or Jacob. But I'm confident that when Juliet sees the grim primary reality, particularly Sawyer, she will reach the same basic realization as George. Ultimately, it's a wonderful LOST after all...
