The flashforward is set-in-stone. It's not a possible future or an alternate reality. Carlton mentions that the flashforwards would be less exciting if they never really happened (I agree). However, we will continue to see more weird time stuff, a la Desmond's time travel. Damon says that "Flashes Before Your Eyes" laid all the ground rules on how time travel works on the series. (Yes, Damon said "time travel." There is time travel on LOST. I hope people start believing this).Interesting, eh? In my review of Through the Looking Glass, I laid out three possible scenarios the flash forward represented. According to the podcast, it seems that scenario #1 (future set in stone, we get to see how it happens) seems the most plausible now. But the fact that they specifically say time travel is possible (and more importantly that Desmond laid the ground rules) gives a glimmer of hope that scenario #2 is also possible (the future really happened, but they can go back in time and alter it).
So what are the ground rules?
1) If you're going to die sometime in the near future, you can't escape that fate
Charlie and Red Shoe Guy proved this one
2) Altering small things in Desmond's visions may change the whole future
Would Desmond have found Penny hanging from the tree had he not saved Charlie? We don't know that yet. But clearly Desmond does have the free will to alter things. Which brings me to the big one...
3) Desmond had a choice in the past. He could have stayed with Penny and everyone would have died.
The big thing here is that Mrs. Hawking didn't tell Desmond that no matter what he does he was going to end up on the island. On the contrary, she had to convince him not to stay with Penny and that pushing the button was more important. Yes, if Desmond had stayed it would have been catastrophically bad, but the point here is he had a choice to stay. And if Desmond has choices when he travels in time, who's to say that he can't go back in time and do it again.
Desmond sacrificed himself when he went back, sacrificed a life of happiness with Penny to save the world. I think he (or maybe Jack) is going to be presented with a similar choice towards the end of show.
Whatcha think? Yea or Nay? :)