I don't think it will make any difference at all. Remember what happened after the "Great Disappointment" in the 1840s, when the Millerites sold up their stuff and went to stand on hilltops in the confidence that the Second Coming was about to take place. After Miller's prophecy failed - twice! - many of his followers fell away, but others simply recalculated and morphed into the Adventists and the JWs, both of which have survived many, many failed prophecies since. My "prophecy" is that the world will keep on going, some believers will find some other entertainment, and the diehards will simply recalculate and move the date onward by a few years. Etc.