Harold Camping, the guy who predicted this event, has done so twice before in the past. He suffered no real loss in followers, insanity, or group suicides, after both predictions were proven to be false.
They've probably already got some excuse lined up, like Jesus just isn't ready yet, or that "the Lord works in mysterious ways!!" You know, the regular religious nonsense.
Yeah, pretty much this. I remember reading about a cult that believed that believed Earth was going to be destroyed by God, in similar fashion to this prediction. When nothing happened, there was an awkward realization of their stupidity that was quickly ended by the leaders saying, "They spared us at the last moment, praise be to God!". And the derp goes on.