I agree with everyone else wait it out, if he doesnt appear he is probably dead. But i do hope you at least find out what happened. Like epsilon said he could be hiding in a rock, we picked up some fish and live rock a few weeks ago and the guys wife kept telling me that there where 2 yellow tail damsels in the tank that morning but i only pulled one out. WEll i put the LR in a cooler filled with SW to keep it live and it sat for a good 4 hours while i redid the Lionfish tank and set up the new wrasse tank. Well i put 3 decent size pieces in the wrasse tank and set him loose and was putting ht rest into the lionfish tank when my girl told me that there was a fish in it. She grabbed him and put him in the reef tank, just glad we notice before i unleashed the lion back into his tank. Just wait it out, takes alot of patience in this hobby.