Eric M Russell (9/23/2016)
After the search effort has completed, there would be no need to gather up all the nanites, they would basically become inert dust after a few days when their power systems drain.
Unfortunately with the power supply or other fuel and lubricants present these would not break down to inert dust. As such they would need to have a return to home mechanism or have some other means of removing them to avoid polluting the environment.
Very useful in open systems though and there is certainly a lot of research and some practical application in fields such as medicine currently.