JOEL - When the repentent missionary submits his papers again, the stake President sends them in to the Church Missionary Department. Keep in mind that close to 1000 mission calls are sent in each week for consideration. After some prayer and discussion, designated members of the Quorum of the Twelve Apostles suggest a preliminary assignment for all missionaries based on a combination of inspiration and the needs of the mission field at the time they receive the recommendations. Mission assignments are then sent to the First Presidency of the Church, who confirms or modifies them on the basis of inspiration. So the initial decision may be based mostly on need but could be altered by inspiration if the First Presidency is so inspired to do so. They make sure that the missionary's calling did come from Heavenly Father and that it is where he was "supposed to be".
The first call that the youg man in question got was where he was supposed to be. But by commiting sin he did not uphold his part of the deal, and someone else had to be sent in his place to fill the assignment. Heavenly Father does not just send missionaries where they are "supposed to be, special for them"; He sends them where He needs them to be at the time they are called. If they are delayed by 6 months to a year, chances are He doesn't need them in the first location anymore but somewhere else.