Pope John XXIII was unexpectedly elected Pope on the 28th of October, 1958. It is widely believed that he was chosen as a 'stop-gap' Pope, an individual who would only hold the position for a short period to give the Church time to groom a successor. It was expected that he would do almost nothing in office and act as a mere placeholder for the next Pope. This particular assumption was proven completely false when he called forth the Second Vatican Council.
Unfortunately, he was diagnosed with stomach cancer on September 23, 1963 and died a few months later. He did not live to see the Council's conclusion in 1965.
What if the Pope did not develop stomach cancer and lived until 1967?