User blog comment:IamJakuhoRaikoben/Chapter 495: I'm Hungry As Hell, Review./@comment-26975670-20160727155715/@comment-7418318-20160727161901

If one of the sisters is killed I'd expect it to be Sorano so she can complete her redemption by sacrificing herself.

But I neither expect nor want that to happen.

If the full set is really necessary, Yukino and Lucy can always join the keys together like they did when they closed the Eclipse or Yukino can give her keys to Lucy without dying. I doubt her Spirits would mind it too much if there's a damn good reason and Alvarez, Zeref and Acnologia make for damn good reasons.