The whole case is silly; in no sensible way was Nicodemus actually surrendering to Murphy. He was very clearly playing her, and I think it was a bit of an author's cop-out to break the sword for it.
And as Uriel says in Changes: whatever you do, do it for love. Murphy did exactly what Uriel recommended, and it worked out (as Uriel suggested), if different than anyone imagined.
I think the point is, yes, Nic was playing her, he was well aware that she had the Sword with her. She didn't know that
except under special conditions, Andriel sees and hears everything, so hiding the Sword only kept it from Harry, not Nic. She couldn't see that she was being played, Harry tried to warn her even as his skull seemingly was about to be crushed. So Nic knowing she had the Sword with her and how she felt about it, he set her up. He did gamble a bit, his gamble was that she'd hold to her belief that he deserved death instead of a chance at redemption... So she raised the Sword, she judged, "damn you," she struck, breaking the rules and the Sword... Now, if she had called his bluff and accepted his surrender, the coin, and the noose, he would have been screwed like Cassius was... Or if he took them back and continued to fight, then she would have been free to lop off his head..
And yes, Murphy was forgiven for her screw up because she did for love... However that didn't make her actions right... I believe what Uriel told Harry in Changes was; page 229 hard back
Uriel said. "Whatever you do, do it for love. If you keep to that, your path will never wander so far from the light that you can never return."
Uriel was telling Harry that becoming Winter Knight if he did for the love of his daughter, his actions would not take him so far off the path, that he could never be redeemed. Yes, love motivated Murphy, yes, it worked out with the Sword... However it remains to be seen whether or not she can make it back to the path to the light. Same goes for Harry as far as that goes. Time will tell.
Well yeah. The idea was never to convince Murphy, or anyone else for that matter, that he was really repentant. If anything, the goal was to do the opposite. He made himself a "defenseless," and "surrendered" captive so that she couldn't kill him with the Sword, then made it blatantly obvious that it was all bullshit and used Dresden to make her really really want to kill him with the Sword, then pushed it till something gave.
Whether or not he was repentant when he surrendered makes no difference.. He surrendered, thus has to be give a second chance at life.. Whether he works at his own redemption or not with what remains of his life is up to him... This is what Michael explained to Harry when he was outraged that he and Sanya would allow Cassius to go free after he surrendered. It isn't for the Knight to judge, yes, if the bastard doesn't surrender, lop off his head, but if he does, he has to be given that chance at life to make amends if he so chooses..