How long must Catholics wait for a new bishop when their old one steps down? There is no definitive answer to that question. In some cases, a new bishop is announced on the day that an outgoing bishop retires. In others, it takes a year or two. Sometimes, dioceses remain leaderless for decades, usually following a major political upheaval. Somalia’s Diocese of Mogadishu, for example, has lain vacant since the assassination of its last incumbent, Bishop Pietro Salvatore Colombo…