Should "The Choice" have a sad ending?

The choice is the story that i'm writing and it's about a teenager and her دوستوں who have powers(oh, beware my overuse of the whole 'superpowers' thing. JK) and in the somewhat middle of the story, She finds out that she has to die in order to save the world. In the original plot, she lived, but I'm deciding to change it up a little bit, and I'm not sure whether یا not to give the story a happy ending یا a sad ending.
link - the fanpop spot.
link - the sneak peak that I put on deviantart.
I REALLY want some of your opinions.