Well I will have to say that clown loaches are excellent hiders. That being said. If it is dead it will stay hidden. I would personally wait a day or two before worrying too much. They are also nocturnal animals and come out more in the dark. so after it being dark for five days straight they might be a little sensitive to the light. Try keeping the lights off and just using the light from the room or a weak flash light to look around once in a while.
Another question is if the tank is by a window or somewhere that sunlight would enter the tank. that would cause some green green water. Just a thought.
I have had clown loaches for four years now. the only time I lost one it jumped out behind the tank and flopped under the stand. I had to use a flashlight and a mirror to find it. That was a very sad day. About 3.5 years ago.. Good luck to you! Hope he comes out..