Odd...
I do know that there are some accension points in the depths that can get you back to the surface. You can also chase down the dragons for a ride back up. So I dont think you are stuck there.
But I don't know why you wouldn't be able to teleport out.
No. No other shrines or towers or roots offer any sort of fast travel option. Ive backed up the saves and started a new game to see if I missed something but can't really be bothered to slog through it again now.