I too like the "replacement goldfish" theory, if we add a cabal of a steering council behind it. It even allows Kavitha remaining on earth and simultanously go into space (why would she abbandon over a billion devout followers, depending on her guidance, since it would surely lead to despair and fall into anarchy).
The inconsequential characterization of Hitchens is, well, a play on Hitchens. Modern sceptics criticize religion mostly on grounds of it being bad for societies, fueling the divide between citizens and ethnies, diverting attention from science to the superstitious and holding progress back. But seeing how in the KP faith seems to further science and unite people to strive together towards a noble goal, he cannot hold his belief that religion would be bad for this society.
Still, we are speaking of northern india here. I can't quite imagine, how muslims (who live there today in spades) would go along with this ("false prophet"), as they would surely see it as blasphemous. There must have happened a genocide of some sort (nuclear or ethnic) for a peaceful KP scenario to be possible at all in this region. Might be another reason Firaxis won't release the specifics of the great mistake, because religious divide is a hot topic today in northern India (especially after the recent elections).