content: I personally don't think that it would be in the best interest of Apple to destroy this software once it's created because the moment the FBI comes to them with a similar case, they'll have to make it all again.  Keeping the software proprietary and under very high security and secrecy would be a better route to travel and would require much less work to be done on Apple's end.  That might even be why the FBI is making this request; it would be more convenient for future cases similar to this, because the FBI could just turn to Apple whenever they have a warrant and probable cause, and everything would be settle immediately.  I'm not always a fan of making things more convenient for the government, but in this case, as long as the judicial system is doing its job and the right warrants are in place, there's nothing to worry about.