you can load a save before this to prep better, do certain tasks around to remove waves of guards from the exit or simply escape through the waterway south by turning the valves in the room next to it (you can use your lockpick if you can't find the key), there is an optional boss down there, but you can easily skip him. if you need details on every stop and route in the dungeon, my guide explains it well, but you can also ask here if needed.