This is a little theory I came up with. I know there are a few loose ends, but it's more Island-specific anyway.
The Island is a constant and everything else (humans, Oceanic 815, etc...) that didn't originate from the Island or wasn't there before Oceanic 815 is a variable. The survivors succeed in exploding Jughead, but the energy under the Swan contains in, just causing the energy to implode into that one spot. That's where the cement wall had to be made.
Now, the survivors will die from the energy in that area. The intense radiation will kill them. No one else is in the area so they won't die, except for Richard. He was watching in the jungle, to see if their plan worked. Presumedly Richard can't die, so he wasn't affected by the radiation.
So on the Island the bomb was the Incident and everything became a loophole there. BUT...They also re-set everything...off the Island. Since the Island is a constant nothing changes. So Oceanic 815 does land and everything is normal. But I do belive that the Universe will course correct of the Island...ie Charlie will drown, Kate will be there when Claire gives birth, etc... And the survivors will be drawn back to the Island, only to find that it's just where they left things off.
Rose and Bernard are Adam and Eve, they died in the cave before 2004. But in 2004 the plane will not crash and none of this would happen again, being another loophole. (Since the Island is a constant.)
The "candidate" is a replacement for Jacob. So when the losties come back to the Island after the reset they will find Frank as Jacob (again the whole course correction thing where Frnak will not pilot 815.)
That is the point where Matthew Fox has said the show will become one linear timeline, and Jack and Locke will face head to head, because Locke will be alive again...but he could in fact meet "himself" (the nemesis) because the nemesis still has the form of his body.
What do you guys think?