It is up to to the Referee to roleplay the NPC according to whatever agenda that NPC has. If the Referee decides that to attack is better than to accept the persuasion terms then he will let the NPC attack with his next action.
I understand that, but if the NPC is going to attack regardless, what is the point of letting the player roll? And you never answered my question on what happens on a Failure or Mishap.
In the book example, the GM had already decided that the Marauder could not be Persuaded. So if Kasia failed the roll, what would the outcome be? What if she rolled two ones? I bet the answer is "The Marauder Attacks"... so why allow the roll at all if you're going to be railroaded into the same answer. The player's actions MUST IMPACT THE GAME in some way... if there are situations where, no matter what, you can't climb the wall, do you let the player keep making Mobility checks? Do you allow it at all?
Or do you inform them of the futility and let them make meaningful choices. Allowing an option and making the Success condition THE SAME AS THE FAILURE CONDITION makes the optoin meaningless.
All I'm saying is allow some kind of "consolation prize" for a successful action that is treated basically like a failure. Apply stress to the Marauder for briefly seeing the humanity of another before launching into an attack. Give Kasia a free Fast action to leap into cover when she notices her pleas fall on deaf ears. Make the success MEAN SOMETHING.