I hope Nomura has thought of something really innovative for the ending.Riku and/or Sora failing is very predictable. Xehanort coming back is already confirmed, it's not the shocking ending for 3D, it was the shocking ending for re:coded. I think Yen Sid being 'killed' (like the way Eraqus was struck down) by Riku who is being manipulated by Xehanort would be a bit of a shocker, kinda like what happened with Terra, and Mickey would try to stop him but be easily brushed aside and could only look on in horror on the floor of the mysterious tower as his master was removed from existence would be really good.. I think it would be a pretty epic scene, but not worthy enough to be the great shocker ending.