In the history of the Church since the days of Joseph Smith, the Lord has always seen that there were apostles ordained to take the place of the Church president when he passes away. My question to you is does a man have to be an apostle to become the next prophet? Why can’t the Lord choose one of the seventy, or high priest or an elder to lead as they all hold the high priesthood? D&C 43:3-4 refers to the gift. Is the gift the office of Apostle?
D&C 43:3-4 states
And this ye shall know assuredly—that there is none other appointed unto you to receive commandments and revelations until he be taken, if he abide in me. But verily, verily, I say unto you, that none else shall be appointed unto this gift except it be through him; for if it be taken from him he shall not have power except to appoint another in his stead.
The gift spoken of here is the authority and power to “receive commandments and revelation” (v3) “for a law unto my church” (v2). As noted in the revelation, there is only one at any time on the earth with this authority. This President-Prophet leads the presiding quorum of the Church of Jesus Christ of Latter-day Saints. If he should fall into transgression (fail to “abide in me”) then the Church’s governing documents specify what happens next.
And inasmuch as a President of the High Priesthood shall transgress, he shall be had in remembrance before the common council of the church, who shall be assisted by twelve counselors of the High Priesthood; And their decision upon his head shall be an end of controversy concerning him.
If this council finds that the President is in transgression, then his revelations and commandments will no longer be binding upon the Church except for one single action: he may appoint a successor (“he shall not have power except to appoint another in his stead” – 43:4). For what it’s worth, Joseph Smith was called before such a council, but they found he wasn’t guilty of the accusation and that was “an end of controversy concerning him”. (see History of the Church 2:142:143).
Now, as for the office of the Presidet-Prophet (and the entire First Presidency for that matter), I’ve already cited some scripture referring to this position as the “President of the High Priesthood.” In the revelation on priesthood, it speaks of the quorum of the First Presidency.
Of the Melchizedek Priesthood, three Presiding High Priests, chosen by the body, appointed and ordained to that office, and upheld by the confidence, faith, and prayer of the church, form a quorum of the Presidency of the Church.
The office required to be a member of the First Presidency is that of a high priest. In fact, Joseph Smith had numerous counselors who weren’t apostles! Any worthy high priest may be selected through revelation to lead the Church (and, if that man isn’t a high priest he’s only a short blessing away from getting ordained). In practice, however, what happens is that at the death of the Prophet and the dissolution of the First Presidency, the Quorum of the 12 Apostles becomes the governing quorum of the Church. This quorum prayerfully determines if the First Presidency should be reorganized, and who will be president. As noted, they may select any high priest, but the Lord in His wisdom typically trains His Prophets for decades in preparation for presiding. For instance, President Russell M. Nelson served in the Quorum of the 12 (with all the various leading councils that that entails) for almost 34 years before he was called as Prophet. President Thomas S. Monson before him, served in the Quorum of the 12 for 22 years and in the First Presidency for another 23 years before his call to lead the Church. With four and a half decades of training, is it any wonder that the Quorum of the 12 selected President Monson to serve as President of the High Priesthood?! That’s not to say that someone other than the senior apostle could be chosen, but there is a great amount of wisdom in this unwritten order of things.