Did you quicksave again? If not, try exiting the game completely, start it again and load your quicksave. That may avoid the missing ladders (this probably will not help in any saves made after the problem occurred).
Periodic new saves are always a good idea.
If you email Larian about this they should be able to edit your save to put your character outside the tunnels (assuming you've done everything there and gotten the fourth amulet), but it would probably be faster to redo the 2 hours from the last auto save.
BTW this problem with missing ladders / sealed doors quicksaving indoors is a known issue, and I would think should be fixed in the next patch, whenever that is released.