Let's start by saying: this is a what if, a speculation. I don't necessarily believe it, but thought it was interesting and wanted to hear the thoughts of the community.
Actually, let's start by saying: this is a loooooong post. Just so you know. Okay! Away we go.
Humans tend to see agency whether it's there or not. We always think there's someone responsible for everything that happens. We're always looking to place blame.
So, when we hear a statement like "The Island isn't done with you" we hear "The Island has plans for you". But what if that's not the case? What if the Island has no consciousness, no thoughts?
Have you heard the idea the Island might be like an anchor in time? I'm not sure where I heard it. I think many people have had a similar thought. (I'm not trying to steal anyone's idea, big apologies if someone else has said this. I don't remember reading this here, but I don't read every day.) Basically, in this hypothesis, the Island is a point which exists in all moments in time simultaneously. The fact it seems to move around the planet is actually the result of the Island staying still, while the planet moves. The "slippery" nature of time on the Island would have something to do with this as well. Structures, people, or anything not part of the Island belong to specific time periods, but the Island does not. (This raises the question of whether the Others have actually become "part" of the Island somehow.) So the Island ends up being a thing through which all moments of history pass, in which case it is like a judge of time, "making sure" things happen as they're "supposed to" happen.
Why all the quotes? It's that agency thing. English isn't very good at conveying unconscious things "doing stuff" without making it seem those things are conscious. What if it simply boils down to the tired old "Whatever happened, happened" argument? The Island may just be the unconscious judge, the gravity-like force which acts as a rudder in the river of time, keeping history from getting off-course and causing a universe-ending paradox. Little things can change, but the Island will course correct, putting things back as close to how they were "supposed" to be as possible. This means Charlie may survive a while, but if his being alive will affect the timeline in such a way as to cause a paradox, there will be a point beyond which Charlie simply cannot survive. A point of no return, if you will.
Why did Michael walk into the street when he was determined to get his son back? He was from New York. Even in a heightened emotional state he would remember not to walk into the street. Except that he's a pawn of the timeline. He can't get Walt back because he DOESN'T get Walt back until later. So it just doesn't happen. Ditto all the guns which refuse to go off when pointed at Michael's skull. Until the bomb, Michael can't die, because he dies in the explosion. Not a plan, just a physical force of the universe (...though it may be incorporated into someone ELSE'S plans...).
Further evidence of this can be found in Eloise Hawking. When she was young, she met time-travelers. Twenty-odd years later, she killed her adult son before he was born. She attempted to change this by doing an incredibly drastic thing: she helped other time-travelers detonate an atomic bomb.
Fast forward some years. Eloise tells Daniel he has no choice but to quit the piano and focus on science. She forces him to be disciplined, keeping his life on a specific path. Later, she sends him to the Island, where she knows she's already killed him. She also meets Desmond, and tries to explain to him no matter what one does, the things which are meant to happen will happen. She has helped people explode a nuclear device in order to change time, and she tells Desmond there's nothing you can do to change things. The universe will "make sure" things turn out as they're "meant" to be.
(Of course, this could all be that she wants things to turn out a certain way, that she's manipulating things, etc. I know. The only evidence for that theory, though, is the lack of evidence as to what Jughead did or didn't do. And a lack of evidence isn't evidence.)
Course correction does afford ONE opportunity for things to change, though. Have any of you read the EW Lost stuff? Dr. Professor whatever-his-name-is said something interesting: Jughead could have been such a cataclysmic event that in order to course correct the Island will have to change some major things. So some dead people could come back to life, some events of the past could change. Not sure what I think about this.
A point I'd like to make in closing, though, might be: time is just one aspect of Lost. Important, yes, but just an aspect. The show seems actually to be about a struggle between Light and Dark, with the Losties as pawns caught in said struggle. Part of what they're caught in is the current of time, but there are obviously other forces. While they are supremely powerless against them all, I think we're about to see them do some major stuff to make sure the "wrong side" doesn't win. Including, possibly, a number of them sacrificing their lives.
So, for those of you who have made it to the end: what do you think?