Keeping in mind that nearly every time I've tried to predict a plot twist in Lost, I've been wrong, here is what I expect will be the result of the explosion that ended the Fifth Season. I'm only attempting to predict what will happen in the first five minutes, but if you don't want to read it now, save it for tomorrow to see if I was right!
The Losties were trying to change the future (or present) by setting off a bomb back in 1977, hoping to change the events that led to their plane crashing on Sep 22, 2004. According to The Rules, what has happened, happened. It can't be changed. That's according to Daniel Faraday.
Now Ben has been going around whining that someone changed The Rules, but he seemed to be talking about a different set of Rules.
And then there is Desmond, who is a "magical exception" to The Rules regarding time. He has the ability to change the past. But he wasn't on The Island in 1977 at the time of The Incident (i.e., the explosion).
Meanwhile the producers of the show (remember Damon Lindelof and Carlton Cuse are going to be on Jimmy Kimmel tonight; set your DVRs!) have been doing everything they can to hint that the past was changed and thus the plane crash never happened.
Here is how I think tonight's episode will start. It will appear for a while that the explosion succeeded in changing the past; you will see the Losties on the plane enduring some turbulence, the turbulence will subside, and everyone will breathe a sigh of relief. No plane crash!
And then the viewers will realize that they've been conned yet again! The turbulence they've just shown occurred at an earlier point in the flight; the real turbulence (i.e., that caused by Desmond's being late in pressing the button in the hatch) is yet to come.
So the explosion didn't change the past; the explosion caused the need for the hatch to be built as a way to control The Island's energy and thus the need to keep pressing the button to diffuse that energy.
So the explosion will be shown to be the cause (27 years in the future) of their plane crash. The Losties will have set in motion the events that will cause their plane to crash.
