I encountered the same issue as well. Was in the middle of leaving a dungeon (Atanaz Ruins) before I encountered an infinite loading screen. Hot exited the game but then I couldn't log back in. Tried multiple times and decided to give it a break. When I did log back in an hour or so later, I was outside the entrance to the dungeon, but noticed that all the loot and experience I obtained within, the skyshard I absorbed, the quest I picked up, and the boss I killed "didn't happen." So now I have to do it again. At least this doesn't happen often. I don't know how far it rolled back though... hopefully it was just this dungeon and not the past hour or so of questing.