No, that's it, the end of the cave... you swim for like 2 seconds and then you're back out into the map. The only trooper left is the one at the very top of the cave, at the peak of the mountain, where you first go inside. The end of the cave where you fight the lakelurk king is where all the dead troopers are, that's the end of it, with the exit being through the underwater bit. So basically you did the entire cave and then chickened out when you saw the exit...