When someone goes missing
Sometimes residents can't be found in one's head. This can be extremely disconcerting for all parties involved.
Having one or more residents go missing is just like looking around to find that one or more members of your family has suddenly vanished without leaving a note or saying anything. When this happens, it might only be annoying, or it might be very traumatic.
Taking steps to keep this from happening, if it's a problem, is the best solution.
Just like in a family, the simplest way of limiting this from happening is to have House Rules that anyone who is going somewhere let others know what they are doing. If the resident leaving is trustworthy and the system's structure allows, this may be as simple as telling one other person that they are going to be unreachable for a while. It may be as complex as having to appear before a council with a detailed report of the planned activities while they are out of touch if more restrictions are in place.
Sometimes, the resident doesn't want anyone to know where they've gone or leaving word isn't an option.