The line could be anywhere and would very much depend on the passage itself and how much visibility the diver had when they laid it.
Indeed, when the diver eventually found the line again, they could be in a situation where they don't know which direction is out. Often divers put markers on the line when they originally lay it (bits of tape shaped as arrows, actual plastic arrows or 2 cable ties together of different lengths), which can hopefully give somebody an indication of the way out. Alternatively the diver could try one direction and see if any of the features on the line (for example line belays or walls or features on the floor) are familiar, or try and find an area with better visibility to then use a compass.
Non of this is ideal though, hence the emphasis on not loosing the line!
Indeed, when the diver eventually found the line again, they could be in a situation where they don't know which direction is out. Often divers put markers on the line when they originally lay it (bits of tape shaped as arrows, actual plastic arrows or 2 cable ties together of different lengths), which can hopefully give somebody an indication of the way out. Alternatively the diver could try one direction and see if any of the features on the line (for example line belays or walls or features on the floor) are familiar, or try and find an area with better visibility to then use a compass.
Non of this is ideal though, hence the emphasis on not loosing the line!