I like the character, don't get me wrong. But I think the writing demands it.
It is one thing to be able to tell a story and skillfully act out emotions and conflicts and surprises on screen. It is quite another to make the audience actually feel what the characters themselves are feeling. I think these writers have proven that they are up to it. They also have proven that they have a few tricks up their sleeves.
Go back a few weeks. Ben is standing in a house in New Otherton. Keemy has Alex at gunpoint. He is threatening to kill her if Ben doesn't surrender. Ben, however, is supremely confident that everything will be OK and the situation is under control. Why? Because he has seen a role that Alex has yet to play in the future. He knows she won't be killed because the island still has work for her to do.
It's like Michael, who we have seen escape death four times now (car crash, suicide, "not yet" bomb, Keemy pulling the trigger at point blank range) or Jack who has escaped at least once (jumping off a bridge) or Locke who has defied the odds at least twice (falling out an 8-story window, being shot by Ben) -- the rules of the universe are that you cannot be killed until it is "your time" -- and if you still have work to do in the future, it is not yet your time.
So Ben knew that Alex would be safe, until... BAM! Someone changed the rules.
What do you think Ben was feeling in that moment? He had seen Alex's role in the future. He loved Alex and had invested so much into her survival. Then suddenly, without warning, she was gone -- stollen away before her time. This is a significant turn in the story -- the rules have changed -- how do you live in a world where the rules have changed -- what do you do?
A perfect cliffhanger for a season finale, wouldn't you say?
So if you were a writer, how would try to get the audience to feel what Ben had felt when the rules changed? Well, first you would have to give the audience the ability to see the kinds of things that Ben can see -- you would have to introduce flash-forwards as a storytelling device (check). Then you would have to create a sense of security for a few beloved characters -- let the audience know that these people are safe in the "now" because they have seen them in the future -- make the audience emotionally invest (check). Then you would have to unexpectedly kill one of them -- you would have to change the rules.
Since the beginning of season 4 we have seen 8 characters in flash-forwards: Jack, Kate, Hurley, Sayid, Sun, Aaron, Ben, Widmore. If you were a writer, which would you kill to create the "changing the rules" emotional effect?
I think we can rule out Ben and Widmore right off the bat. They are both too central to the overall story, and there is apparently something larger happening between them where they cannot kill the other person, otherwise Ben would have just killed Widmore in that bedroom and not bothered threatening Penny (interestingly enough, so that Widmore could feel the rules-changing loss that he had felt). I'll give these two a 2% chance of being killed in the season finale, although I also acknowledge my bias here -- I really want them to survive.
Aaron would be a very weak choice for death. No one has invested much in Aaron's future role at all, and the reaction to his being included among the oceanic six was just this side of Nicki and Paolo pretending they had been part of the cast since the beginning. Killing Aaron would be an easy character to kill, but it would not have the desired emotional impact. (10% chance of being killed).
I think we can rule out Sun. She bought a controlling share in her dad's company and she has unresolved issues with Jin's apparent death. There are still loose ends to be tied and we have an emotional investment here, but there has not been enough clarification on her future role to make her a signifiant candidate. (20% chance)
I think we can rule out Kate and Hurley because they are too central to the show emotionally. Yes, that means it would come as quite a shock, but I don't see that the writers have developed much of a role for them this season for the overall scheme of things. Besides, I think the public outcry in killing them off would be too great. But again, aside from Kate raising Aaron and Hurley having the ability to see Charlie (and Jacob's cabin), we haven't really been asked to make much investment in their future roles. (25% chance)
I think we can rule out Jack along with Ben and Widmore, because he is too central to the story as well. That said, however, it would certainly be a massive shock, which makes him a strong candidate for an emotionally-charged, rules-changing death. But Jack has to get back to the island to correct his mistakes and play his destined role in overthrowing Ben. As tempting as it would be, I wouldn't off Jack. (40% chance)
So that leaves us with Sayid, and he matches all the criteria perfectly (which is no accident, to be honest, since I created the criteria with Sayid specifically in mind). We have seen him twice as an assasin in flash-forwards, so we know his role very well. We have been given the emotional investment with his marriage to long-lost-love Nadia. And best of all, no one would ever suspect it. He is the perfect central-yet-not-so-central character for this kind of emotional payoff. (51% chance).
The writers have promised that in the finale we would find out who is in the coffin. After all the speculation that it is Michael or Sawyer or Ben, wouldn't it just freeze those donkey wheels right off you to find out it was Sayid?