Why would the toolbox be due to deorbit? Its orbit should be as stable as the ISS's, or did it move towards or away from the earth with enough velocity to significantly change it's perigee to interface with the atmosphere in such a way as to deorbit faster than the ISS? (or does the ISS have thrusters to prevent this?) After a finite number of orbits, shouldn't the toolbox come back towards the ISS?

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"What you think you thought you saw you did not see." Agent J, MiB - Manhatten Bureau