For something this ‘unbelievable’, (it actually is pretty believable) I must give sources first. This page has a simple translation of a December 2001 article in an Egyptian newspaper where Osama’s death was given. This page has more information, including a picture of the original newspaper and a picture of a pretty sickly Osama in a December 2001 tape.
Of-course, it makes sense to perpetuate the myth of a living Osama who can serve as both a casus belli for more wars and a bogeyman to keep the Americans brainwashed in fear. Disinter is right in tagging his entry on this with ‘fear-mongers’ and ‘war profiteering’.