I thought the sword fight at the end was awesome. Sure, we knew neither was going to be seriously harmed.
speak for yourself. This is a show that killed off its main star 8 episodes into its fist season.
Well I didn't know, but it just didn't feel like it was right for either character to go down. Both have so much more that they can accomplish within the story. As for Ned, the only reason we thought he would escape was because "that is what is supposed to happen" in these epic tales. If you look at the facts of the story, Ned was a clear dead man.
ETA: Also, it didn't really benefit either person to kill the other. If Kingslayer dies, Brienne has totally failed her mission (as he pointed out). If Kinglsayer kills her, he is now all alone in the middle of the kingdom. He is better off with Brienne because she has his back in case they stumble onto some trouble. She is taking him to Kings Landing, it's not like she is marching him to wall or anything. She is trying to free him. The fight was a pissing contest and a way for Lannister to entertain himself.