This happened to me last night on a normal pledge.

The Chamber Guardian's attack sent me and him through the wall to the left of the doorway. He returned to the fight, I remained stuck outside the walls.

Now, I know the correct method to fix this. My teammates kill the boss, I "travel to player" or /stuck and end up at the beginning of the dungeon, portal to the group and we go on our merry way.

This time since I was running the dungeon with friends, I decided to explore. From where I'd ended up, I could clearly see into the rooms of the dungeons. Outside, a purpleish cloudy void waited. Of course, I leapt off the edge.

There's a lower, undetailed level to the Crypt of Hearts, a bedrock of purple (ebony?) rock where I landed. There are a few spikes of rock, but beyond the bulk of it on which the Crypts rest, there is a short, shelf-like ledge on which I found myself only a few steps away from the eternal void with its light purple clouds in the distance. Of course, I leapt off the edge.

I found myself falling, eternally, down the side of a long flat wall of that ebony texture. /reloadui did nothing, so I finally appealed to the mercy of ZOS with /stuck and then, as the wall vanished and I was free-falling into the endless void, ZOS saved me and deposited me back at the beginning of the dungeon where I portaled to my friends and we continued on.

10/10 would do again.