Okay remember when Keamy shot Alex? That sucked, right.
But besides allowing us to see Ben show some real emotion, the best thing about that horrible, horrible scene was the "he changed the rules" mindfuck.

What rules?

Well, the crazy theory I read is this: it was not a simple thing like "no hurting Ben's family." It was because Ben knew that Alex couldn't die. Yet she did. The rules were broken.

Why did he believe she couldn't die? Because he knew she was alive in the future.

This ties in several mysteries.

First, there is the time-weirdness that's been building up all season. Time acts weird on the island. Faraday's experiment, the time-slipping caused by improper approach, and foremost the doctor being found dead before he died. This is all pretty weird and it *must* have some deep significance.

Second, the idea of "course-correcting." This was introduced with Desmond in season 3. He knew Charlie was going to die... and no matter how many times he tried to stop it, YER GUNNA DIEY CHAR-LEY! And Desmond's flashes were caused by the electromagentic release reacting with the time-bubble of the island (remember the comment in The Constant, "Has he been near any electromagnetism?" or somesuch.)

Third, Michael's suicides. Tom said the island wouldn't let him do it. It's not that he couldn't kill himself, it's that he couldn't die, period. I think that he is alive at some point in the future (I think he'll have to return to the island) and the universe will course-correct to make sure that happens. Perhaps he dies on the Island- which is on a different time-stream- and thus can't die in the "real world" because that would create a paradox.

Basically: the island fucks with time, creating loopholes for paradoxes... but these paradoxes are prevented.

Until Keamy shoots Alex.

Now, I doubt Widmore could somehow change the paradox-solving properties of the Island. What I believe is that at some point- in some future, something important happens involving Alex. Whatever this is, it's important, and both Linus and Widmore know about it. Perhaps they came to some agreement about it. That whatever happened- in their fight over the island- they would make sure the peices would fall into place for that event to take place. Alex is probably not the only necessary element.

So at some point, Widmore reneged on the agreement. He told Keamy he could use Alex as a final bargaining chip. With her dead, the future can't go the way it was supposed to. Of course, you'll ask why the universe didn't course-correct, and jam Keamy's gun, like it did when he tried to kill Michael. I'm not sure.

So that's the theory... hopefully the finale will confirm/deny at least some of it.