Perhaps the use of the word 'disappeared,' as it applies to people, is misplaced. We take that to mean that the individual simply vanishes without a trace, reason or explanation. One post above, where two people suddenly left thge ship under 'mysterious' circumstances, comes close, but simply vanishing without a trace is another matter. We've been on trips where people had to leave the trip, unfortunately, for medical reasons( in two cases, they later rejoined the trip ), but no one has simply vanished without a trace.
Similarly, there have been posts where personal articles have apparently been, unfortunately, stolen, but we don't recall ever seeing any post where something simply vanished without a trace or explanation. Even in the thread Pauline mentions, the passport wasn't confiscated, as we take the word to mean; the word was used inappropriately by a traveler who simply wanted to make a point.