When it comes to the narrative flow of the game there's not really hard and fast rules. Sometimes it depends on what the NPC is risking. A random NPC who isn't going lose much getting taken out isn't going to give it his all. That, and if this conflict isn't important to the story then why waste time on it?
Let's say it's a social conflict with a bouncer to learn if someone has entered the bar. Why would the bouncer take a consequence over something like that? Just do a resources maneuver to place the aspect "There's money in it for you" and take him out socially - probably in one exchange.
Now if it really mattered to him - say he was the target's brother or had been developed with the high concept of "Tough Ass Bouncer" or something like that, then things would be different. Of course then he wouldn't be a random NPC - he'd be a step above a mook and take consequence to keep that information to himself. Call it two or three exchanges.
If he's secretly the Darkness Given Form, or a Seelie knight impersonating the bouncer, or otherwise plays an important role in the game, then he should be resisting the contest as well as any PC could.
Amber Diceless Role Playing had a guide for how to handle conflicts - unimportant ones get brushed over while the important ones get as much focus as you can give them. That game cited the amber novels. There's a place where there is four or five pages of thrust, counter thrust, riposte, feint, some footwork, some verbal fake out, etc that was two almost equally matched main characters dueling. That fight was important so it was the focus of the narrative for quite a while. Then there's battle scenes where:
"Three more men plummeted past me and we came to a small landing and a turn. He cleared the landing and began the ascent. For half an hour I watched him, and they died and they died. "
Yes, that a great warrior killing 50 or 100 guys in a couple of sentences as he fights his way up a single file stairway that's carved into a cliff. None of those guys were important to the plot so they just died - simple as that. They got lucky here and there and slowed the guy down a bit - and once there was a chance the great warrior might fall things were broken down a bit more, but walking half a mile up a cliff stair, killing a man on each step? Call it a page to a page and half.
In Dresden it's the same way. If the character or struggle is important to the plot then fight it out, otherwise fill the mook's stress chart and go on to the next one.
Hope this helps.
Richard
PS: I'm going to have to start typing faster and was I thinking about deleting this post when he saw the advice above saying the same thing - but added this footnote instead.
