After Jack's death by Clarence Moy

Not really sure this is a theory, but more a summary of what happend after Jack died in the jungle next to Vincent. Obviously we saw the plane fly off the island, and the Hurley-Ben era began on the island. Something interesting Christian Shephard said to Jack, that everyone in the so called "alternate time line" died either before Jack or much after Jack had died. This tells me the people who got off the island along with Ben, Hurley, and Desmond lived a long full life. Hurley probably changed many rules allowing his friends, Sawyer, Kate, Miles, etc. to come and go from the island after they had left. Hurley probably got Desmond back to the real world to be with Penny. Nothing significant happend after Jack's death which is why the show ended with his death, as this was the last iconic and memorable event to happen on the island and in the characters lives.

As a die hard fan, I would love to have known what happend to the characters after Jack died, but the way the characters (Sawyer, Kate, Hurley, Ben, Desmond) seemed to react after realizing their island lives in the alternate world showed everyone was happy with their lives after Jack died. As for the people who died (Sun, Jin, Juliet, etc.) them just being with everyone on the island was their best experience ever, as said by Christian, was enough for everyone being satisfied with the "Afterlife".