People are still confused on what to take from the enhanced episodes of LOST. Some believe that it is merely "marketing department" annotations and not canon material. Others believe that TPTB have to have some input into the screen crawls otherwise their work could be contaminated with non-canon material. TPTB never denounced any of the enhanced materials. However, ABC admitted that it added the plane crash scenes over the End credits.
Now, the sideways world was subtitled as "what if" time line if Flight 815 never crashed on the island. In the End, we find out that if "what if" was fantasy, then that is correct. The sideways world was a made-up construct from the 815ers collective memories as a place to meet in the afterlife. (Who, what, when, where and how this occurred is a complete mystery.)
Next, the enhanced episodes stated that Juliet died when Jughead, the h-bomb, "went off." This is the apparent "Incident" that changed the course of the island events. If one suspends disbelief that a hydrogen bomb can be detonated by a rock, then how did Juliet not vaporize? How did all of the 815ers survive radiation fall-out and the shock wave? Further, the blast door map said the Incident happened in 1985; not when Juliet hit the device in 1977. If the bomb did go off, then the island world was not "real," but the illusion of reality. No one would have survived. If the bomb did not go off, and the drill hit an EM pocket that caused the sky to turn purple (and time flashed back to 2007), based on past experiences, the 815ers could have survived the jump. But that itself, does not put the island in the real world.
The problem with the island world is that light source and EM was never explained to any degree to determine what exactly is the island. Is the light source and the EM part of the same energy pocket? What is the energy pocket? What causes the EM and its "unique" properties? Why would you need to release the EM build up in the Hatch, but not in the island cave (the heart of the island) near the bamboo grove? And if an atomic bomb did go off, what changed? The sideways "events" were not created by the bomb, but according to Christian, it was made up by memories.
The whole mission to detonate Jughead appears to be a story dead end. It is one of many story line dead ends: why the Egyptian sets? who were the Others? what was Dharma really doing? what was the smoke monster? what was the lighthouse? what were Hanso, Widmore and Paik industries roles in the island? None of these story elements had any true relevance or material implications in the LOST ending of the characters being reunited in the church.