How to get into Offline Mode - Patch 4.1
Proprieties of Offline Mode:
-Offline on Battle.Net
-No NPC's and no other players
-Cannot cast any spells, change map, queue for instances/bgs, logout, exit game (you have to Alt-F4)
-You take no fall damage, no fatigue
-Invisible in Guild Chat but can talk and can see what everyone else is writing
-If anyone does a /who on you, you appear unguilded
-If you are invited to a party, the other players will see that you are Phased
-Upon relogging, you will be alive at the graveyard