What happened to the followers of William Miller when Christ did not return on October 22, 1844? Did they go back to the Bible and the Churches?
No, many gave up on the Bible and Christianity altogether; many became enamoured with the Jehovah's Witnesses and their (false) prophecies, while others became Second Day Adventists under the "ministry" of Ellen White (who herself was very impressed with Miller).
What does this teach us?
It teaches us that the deceptive spirit behind Harold Camping's teachings will still be very active, even after May 21 comes and goes. He already has them in his snare. Only God can reach these precious people, deceived by the deceiver.
Let us preach the truth with compassion and boldness and pray for God to open eyes.