Although celebrities function as the necessary human face for corporate bodies, they are still loose cannons. They have off days, can cause unwanted controversy and can't be controlled and shaped completely. Corporations still have to work with them and be patient to some degree. Celebrities are also pretty expensive, and they age and eventually die.
Top tier celebrities may as well not exist. To the masses they may as well be virtual, as most of us will most likely never see them in any kind of believable proximity. Eventually there will arise a virtual celebrity capable of fulfilling all the roles and demands our current tabloid royalty face, but without complaint, and for a lot less money too.
They will be able to go to Mars and back, skype us from the ISS, be able to speak any language fluently, have personalities that will be much more encompassing and appealing to more demographics than the sparkling apparitions we currently spend our days looking through in lifestyle magazines.
On a realistic level, the best way I can think of to bring humanity together is the threat of a massive fuck off asteroid that is big enough to destroy the Earth if it strikes, but still small enough to be taken out if we all join forces. This scenario incarnates the mantra "We only get one go at life".
In a similar sense, when the first global virtual celebrity starts encroaching upon and then usurping the role of its meat-filled contemporaries, celebrities as we know them now will become mortals again. Ironically, they'll come back down to Earth and join us plebs in the chorus against worship of a God that isn't real.