IMHO, the great "Falling away" ie "Departure of the faith" is already happening... Look at all the rampant apostasy, and heretical teachings going on. The occult invasion of the Church, homosexual preachers, so-called "Liberal Christians" (Which is an utter oxymoron) and prosperity preachers.
The evidence of the Laodicean Church is everywhere. A real christian will rather die, than take the mark of Antichrist. So belief in the rapture, or lack thereof will not be the cause of apostasy. Apostasy comes forth from people who are not true to the faith. A Good tree, cannot bear evil fruit. See Matthew 7.