User blog comment:Fimber/Background stories that have been ignored?.../@comment-3325613-20120902171057

I think there's a little difference between "You have a destiny, you've got to do something in your future" and "you cannot die, you're invincible". In "The Poisoned Chalice" Nimueh told Arthur it wasn't his destiny to die at her hand, but she didn't have any problems leaving him to die anyway. She even tried to kill Merlin in "Le Morte d'Arthur", thinking she could replace him as Arthur's guardian and future creator of Albion. As far as I'm concerned, being there a prophecy about Merlin's destiny doesn't mean that the future cannot change if he dies. As Morgause herself told Morgana: "There are many futures in this world".

As for Uther knowing about Morgana's powers, I find a deleted scene from 3X13 very interesting. There, while he's in the dungeons, Uther tells Morgana: "I'd have Morgause and her magic for corrupting you", at which she replies: "[...] I didn't choose my gifts, just like I didn't choose my father". So even if he hadn't known about Morgana's magic before her alliance with Morgause was revealed, he must have realised while he was kept prisoner.