He could very likely be hiding in a hole in a rock or something. With all the activity of moving tanks and dipping stuff he just might be needing some quiet time to himself and will surface we he feels like it.
It is also possible that he may have perished due to the stress of everything and at that size it likely wouldnt take long for the body to disappear to nothing.
But I would just keep an eye, many times I have heard of wrasses seemly disappearing from a tank only to show up a week or more later alive and well.