ALTERNATE TIMELINE NOT AN ALTERNATE AT ALL by Geoffrey Lawson

This theory erases all paradoxes and creates one unified timeline - a single quantum theory of time travel. What if jughead did not split the timeline at all but simply brought the characters back to 2007? The off island sequence in 2005 that we are watching is something entirely different shown in tandem with the on island sequence of 2007 to setup a big reveal at the end of the season.

Each character on the island is brought to the island by Jacob when they are needed. When are no longer needed, they "die" and return to "real time". What we are watching this season, off island, is the end of the entire series. Once the characters die in the battle between Jacob and MIB on island, their consciousness will flash back to Flight 815 in 2005 (or this same sequence at a later point) where the were always suppose to be. When Juliet said "it worked" as she was dying, it was because her consciousness in 1977 was in the process of flashing to her "real timeline" off island where she was alive.

(This theory also leads to the idea that the losties were never suppose to leave the island. If any timeline was at all "alternate" it was when they left the island during Season 4-5).