Munden would still smoke the guy. Just because he doesn't kill people for a living doesn't mean that his training wouldn't take over. You aren't a killer until you are. No reason the first time would be slow, or that he would waver. Munden's skill far surpasses that of this hit man. I have seen many men who never shot anyone turn into calm, professional killers because they fell back on their training.
Now, the after-effects? They can have a lasting impact.