John Hyde says the penalty for adultery amongst endowed LDS is death.
John Hyde, Mormonism Its Leaders and Designs (New York: W.P. Fetridge & Company, 1857), 108
The penalty of adultery is death. Dr. Vaughan was shot by a Mr. Hamilton, on suspicion. James Monroe was murdered by a Howard Egan, for the same reason. Should an endowed Mormon commit adultery he must die for his salvation. If a Gentile, he must die for atonement.