To my knowledge, all R51 Pathfinders with four-wheel drive and are "LE" trims have the AUTO mode transfer case. I've never heard of nor seen one without it. So, you might want to make sure it is an LE. LE's will have the Bose system, leather interior, faux wood trim at the door switches and center console trim, climate control, sunroof, roof rails and side rails, auto lamps and, if I'm not mistaken, fog lamps, as well.
I leave mine in AUTO mode all the time unless I'm running on unplowed, snow-covered, roads. The owners manual says to use 2WD mode for best gas mileage, but my testing shows there's no difference and I really wouldn't expect to see much difference since AUTO defaults to 2WD most of the time, anyway. So, the only difference between AUTO and 2WD mode the majority of the time is that AUTO will allow the electric transfer pump to operate at idle, in reverse and speeds under 35 MPH. However, it is nice to have that feature of the transfer case applying power to the front wheels in an unexpected situation to better control traction. It's a nice feature to have when driving in conditions when there are spots of snow or ice on the road but for the most part is clear. I have both an LE and an SE and I prefer the LE's transfer case. I wouldn't call it a deal breaker, however, if choosing between two models and one is nicer but only has the part-time transfer case. Go with the overall, better vehicle unless you really want the other options the LE provides, as well.