This idea held by a few ex-JWs that the GB secretly know it is all untrue isn't correct. They are all 100% totally convinced- delusional , no doubt but nevertheless absolutely sure that it is "the truth".
It's very unlikely that a Ray Franz type individual would apostasize from the GB now - he was a throwback to the days when the GB had less power , there were 18 odd members , members were appointed to an extent on their bible knowledge & scholarly ability rather than ass licking skills and the real power was held by Knorr & Fred Franz.