Here are my thoughts on the light....Mom said somthing that it "is something that is in everyone". I am assuming this is physical entity of "Good". She said if someone trys to take it than it would seize to exist. then she said you dont want to go in there because it is worse than death. MiB was forced into "taking" the light by Jacob...Could this explain the bad things that have happened to our Losties (Running from the law, Alchoholics, torture, curses). there is more evil in the world since the light was taken? And if MiB truly finds a way off the island than all chaos will be exposed? Like the State Puff Marshmellow Man? So the island is what is keeping him from leaving. I'm guessing that our losties, Probabaly Jack finds a way to return the Light to its proper place then life is better because of it, this gives you TFST (Jack is a good father, hurley is successful, Locke is content to be wheel chair and had relationship with dad). For the most part their lives are better than what they were to begin with, at least those who have been Loyal to the Island...Jack, Sawyer, Miles, Hurley.
I have been a tough critic on FST but if it works out this way i will be okay with than...I still want there to be life on the island when it si all said and done.