Ooh, goody! Not often I get to involve logic in arguements like these. Ellone can't change the past. Why not? Because the past leads to the present. If she changed the past so that Laguna was there with Raine when she died, she wouldn't have a reason to go back into the past. With no reason to go to the past, Laguna leaves Raine, cycle starts over. The past can't be changed without removing that which changed it. Ergo, no change. Simple as that.