What the move action should be is also dependent on NPC/PC's priorities and the amount of risk they deem acceptable. If survival is number one, simply retreating is a very valid choice; however it is entirely possible that the character has priorities that trump survival (duty, revenge, monetary gain, etc) or a low aversion to risk.Isn't a lot of this example predicated on the barbarian being kind of an idiot? If someone is shooting at you, and you can't see them, your move action should be to get the hell out of there, not stand around and keep looking.
The barbarians intelligence should certainly factor into his choice of action; but running a circle around the object your quarry just hid behind is a fairly simple concept.