Continuity mistake: At the very end of the film when the bed crashes through the wall, Olga has disappeared from the very first outside shot. She is then back to the left of Cato in the next shot. This was likely done because she was completely nude and the audience would've got a good look at her.
Revealing mistake: When the castle starts to disappear at the end, lines are visible on the matte painting where the pieces were. As the remainder of the castle disappears, a significant line in the painting is visible on the left side during the remainder of the shot.
Continuity mistake: During Oktoberfest when Clouseau is being followed by assassins, one has metal spikes in his chest. They change lengths during the scene. They're longer toward the end of the sequence.
Continuity mistake: During the scene when the U.N. building is disappearing, the top of the building changes. Notice in the other shots, there is some sort of structure atop the building. It is see-through. When we see the effect happen, that structure is gone.
Continuity mistake: When Clouseau is on the front page of the newspaper after being arrested in the Soho club the date on the front of the newspaper is Monday July 12th, but two other events in this film are in October, the beer festival and the disappearance of the UN building. The events of the film don't cover that long a timespan.
Continuity mistake: During Clouseau's visit to the asylum, when a completely soaked Dreyfus finally climbs out of the pond, his clothes have only partially wet patches before he sits on the bench and then they're soaked again.
Answer: Just Invisible. Besides the fact that his eyeball and eyelid remain intact and in the same position, he returns in a full, visible form (possibly in a film logic borrowed from Looney Tunes cartoons) in the next Panther film.