Other Popes resigned - one, Celestine V, made a decree in 1294 (around the time Edward I of England was invading Wales and hammering the Scots) - Celestine announced it was OK for a Pope to resign, then put his money where his mouth was and promptly did so.
Apart from him and a Martin who was tortured to death in Byzantium (they took their religion very seriously then), however, there were two other Popes of a retiring nature. Both called Benedict:
Benedict V (964): Forced to stand down by Holy Roman Emperor Otto I, who had another preferred candidate
Benedict IX (1032-45): Sold papacy to his godfather, then had change of mind and tried to seize it back - he was later excommunicated.
(More at the BBC)
Perhaps this Pope would have been more inclined to hang around if he'd selected a different regnal name?
Whoever takes over has one heck of a job on his hands. I wonder if he will manage to drag the Church at least into the twentieth century - the current one is probably too much to hope for.