"A generation" refers to those alive when Jesus spoke those words. That was in 33 AD, and it refers strictly to the end of the Jewish system of things in 70. That was a wait of 37 years, and quite a few that were alive to hear those words in 33 were also alive to see 70.
Then again, it would be hard to hold the religion together if I were to run it with fully integrated honesty. Quite a few would defect (mostly those in it for the power), and there would be some that were in it mindlessly that would accept whatever I put out (even if it was fully honest). But, after the fallout, the paradigm would attract more decent people (not those pedophiles and baby killers/eaters). And, it would be able to stand up against those who study independently or that want open discussion--fully integrated honesty is pretty difficult to knock down with "apostates". True, you would not recognize the religion after I was finished with it. But, from that point on, it would be pretty much apostate-proof.