I kind of see this as a trick question. Although I'm sure thats not what you intended.
If you say yes, then you seem like a selfless hero. If you say no, in any regard, then you seem like a coward who thinks only of him/herself in the end.
I think that we need to look at the logic of such a hypothetical situation.
Lets look at some examples, shall we:
1.) Theres a hostage situation, and you agree to go with the criminal in exchange for the freedom of everyone else. You realize you may die in this whole episode, but there is a chance the police/swat teams will be able to save you.
This situation is sort of a blur for me, as my death is not certain. If my death could be guranteed to not be in vain, I would do it. But for me to come to that conclusion, I have to assume that the criminal plans to let me go, or the cops can save me.
Whether I die or live, I did a noble thing, so I'm guessing that yes, I'd do it.
2.) The "taking a bullet for someone" situation.
This one is even more tricky. As it requires me to think on my feet within seconds. IE- I see the shooter, expect the bullet to be coming, and push the person out of the way or put myself in front of them.
Again, for me, this depends on the person. Are they a homeless person on the verge of death, where perhaps death would be a blessing? Or is this the president of the United States of America? If I'm taking a bullet for the president, then its my job obviously, and I get up every morning realizing this is my destiny as I have chosen it.
If this is like a gang-fight sort of shoot out thing, where its too random and unpredictable, and I have the ability to save someone in a cross-fire, and they're my friend or something, then yes I would do it.
For several key factors. Gang members are lousy shots (thet focus more on how many bullets they shoot versus their accuracy). The confusion of the shootout means that my friend is not an intended target, so I am expecting maybe 1 bullet coming our way in that given moment. The gang members most likely possess a crappy piece that will only cause a flesh wound, and not a mortal one.
If this is the case and all these factors are in my favor, I would take the bullet for my friend. If this is like a drug cartel sort of deal and it's like a major street war and $hit, I'm thinking its a matter of survival period, and I'd try and save us both if there was time. I doubt though that we'd be there in the first place when this is all going down.
3.) Theres a terrorist attack on a plane they've hijacked. I have the time to throw myself at the terrorist and to wrestle the weopon away from him. There is a chance the gun will go off and the following things will happen:
1.) I am shot.
2.) Another passenger is shot.
3.) The terrorist is shot.
As it is close quarters, I doubt he would have time to fire twice. This being the case, I'm thinking that it's worth it to sacrifice myself and potentially another passenger to save the rest. Unless this is like the movie Air Force One, stopping this lone terrorist and his attempt is worth it.
4.) There is a family member or friend who is dying of a disease, and for the purpose of this hypothetical, I have the ability to save them (though I will die).
All of the situations I can readily think of, this would be the one I'd have the easiest time accepting. It's completely of my own will, and not a spur of the moment action. I am concisiously saving another life through an exchange.
I believe as I currently stand with the Lord (or so I hope) that this act of selflessness will be rewarded in Heaven, or, at least cut my time down in Purgatory significantly.
I'd probably be thinking more about my friend or family member than myself during the actual execution of the sacrifice, and hopefully that will spot me some extra points with the big G when I die.
LOL ^__^
In closing, I'm figuring that it's worth it in most circumstances to sacrifice yourself in this way. Chances are good you may survive, unless the situation is so hopeless and dire. It's usually not that way though, so to answer your question, I'm saying yes, I would. (sorry for the long reply, though I hope it was good for you).