I heard in Elder's Quorum that it was not revealed how succession should take place.

D&C 43:1-7 and D&C 124:91-96 tell a different story. A reasonable reading of these verses state that Joseph would appoint a successor, and he did, it was Hyrum. Hyrum was taken also.

Even Brigham Young admits this: "Did Joseph Smith ordain any man to take his place? He did. Who was it? It was Hyrum..." (Brigham Young, Times & Seasons, October 15, 1844, Vol. 5, p. 683.)

Is it possible the saints did not complete the Nauvoo temple in the Lord's appointed "sufficient time" and thereby reap the consequences?