I don't know much about Islamic law
If Osama bin Laden were to take that long leap into oblivion, it'd be amusing to hear all the reports that he has been sighted around the world. Remember how people claimed that Hitler was still alive decades after the war or all of the Elvis sightings? Only, in this case, the powers that be would know the truth.
I can almost hear the transition briefing from one adminstration to another - "You remember bin Laden? Well, he's fish food. Would you like to see the video? If you hear a report that he's been spotted somewhere, you can safely ignore it."