Fountain of Youth Theory!!!
Ok, here goes (starting from the current season):
When the H-bomb went off, it allowed for the pocket of energy to expand not only to the island, but to the entire world
what that did was split the world into 2 realities
in the island reality, they are all doomed. everything is proceeding as normal
in the other reality where their plane never crashes, there is no island because that reality was sent into the distant future where there is no jacob to control them and the island is burried underwater.
the whole point of the island is the fountain of youth
where they tried to heal sayid
the two protectors of the island: jacob and his friend were sent to the island to protect the fountain of youth from corrupting people
they were first sent to egyptian times
their main goal is to keep it safe and not let it fall into the wrong hands because it could mean the end of humanity
so the egyptians built a temple
over time jacob brought others to the island to keep it safe
but it always ended in tragedy
richard is one who drank from the fountain
that is why he never gets old
over time jacob’s friend got tired of living on the island attempting to protect the human race which he believed was beyond saving. eventually he just gave up and wanted to get off the island.
his way off the island is through locke
jacob, now, to protect the island has taken over the body of sayid
i think that it will end with everyone in the island reality dying, but at the same time showing us that the “real world” reality was saved through their death and the chain of events that started w/Oceanic 815 crashing on the island.
yeah, thats the theory
now, whether jacob and his friend are angels sent to protect the island or humans from the future who know of our destruction is another matter…