Well GUS IS the last one... functioning and still running that is. The fact that he is working away, tinkering on the garbage left at the junkyard, is simply left to neglect and abandonment. What does a program do if you leave it running with no job to do? It keeps going trying to continue doing his 'current' job.

GUS will have a symbolistic place in the game, both as a character that helps our hero to upgrade himself with current-day technology and to tell a part of the story of what happened after he went missing. How technology evolved in the world without any of the doctor's works and what path it went instead. Also it shows a darker side of what the Doctor's technology did to the rest of the worlds creations and the sheer power of it's effect on what happened when itwas taken into the wrong hands.

Deep, sad? Symbolic and scary? Yes... it's ment to be.

There will be other characters with as much story detail given to them. GUS is just one of many characters that tell the story.