I did a quick test to see of Oculus Rooms works with Wifi off. It doesn't, citing network troubles. So my guess is the rooms are hosted elsewhere meaning you can't just make a local room to play with buddies when the internet is down/not available.
That's a shame, though possibly something that will work with the next Rift Core update? Oculus announced that in Oculus Home you'll be able to invite friends. Hopefully that will work for local network only as well.