User blog comment:Morganaforever/Is Kilgharrah a good prophet?/@comment-5674726-20121208001120/@comment-5102537-20130525050212

"If it's only after those events that Morgana and Merlin's futures became joined, with her as the darkness to his light, etc, would it not stand to reason that, had Merlin made different choices, that fate could have been averted?"

If it hadn't been for the Vilia saying that Merlin's future has been written since the dawn of time and if Nimueh hadnt obviously chosen Igraine deliberately, which actually led to Merlin and Arthur's destiny/fate/future, I would say yes.

Either the showrunners/writers couldn't decide whether or not the future of everyone was set in stone - or at least one of the characters simply lied and we'll never know. I think it's rather the first option.