Faith, pg. 2; “In the early days of the restoration of the Church, Sidney Rigdon did not retain his membership in the kingdom even though he had, with Joseph Smith, witnessed marvelous signs. Had he not participated in the great vision, and had he not been the recipient of many revelations? Yet despite all these manifestations from our Heavenly Father, he did not remain in the kingdom…Oliver Cowdery saw many signs. He handled the sacred plates; saw John the Baptist; received the higher priesthood from Peter, James, and John; and was the recipient of many great miracles; and yet they could not hold him to the faith.” – Spencer W. Kimball, Also see EM, pg. 1565.
Galatians 5:1; “Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.”
If the original witnesses to the Book of Mormon left the Church, I’d think that would make anyone stop and think about the gravity of this information.