Like any secular monarch, the pope is elected for life but that does not mean that it is impossible for a pope to step down while still alive. This is not a common occurrence because it would affect peoples perception of the stability of their churchs hierarchy and might set a precedent for church factions to pressure popes to resign; yet the possibility of a pope resigning is very real.
There are procedures for removing an incapacitated bishop. Should something happen to him, the diocese is declared as impeded and an auxiliary bishops takes over. Nothing like this exists in canon law for an incapacitated pope, even though he is also Bishop of Rome. The only provisions that exist for dealing with an incapacitated pope is to have a designated cardinal oversee the Vaticans day-to-day operations.
Whats important to understand about the papacy is that the pope is far more important for who he is than for what he does. It is true that a pope does quite a lot, both in administrative matters and as a cleric, but he doesnt actually have to take action in order to be pope. His importance as pope lies in being a symbol of Christian unity. Thus, as long as he is breathing, he continues to fulfill some of the primary duties of his office.
Typically when we read about papal resignations, media experts tell us that the only pope to ever resign was Celestine V in 1294. This is untrue in many ways: Celestine was not first pope to resign, nor was he the last. Celestine is, however, the pope who created the official procedure by which a pope can resign, so singling him out is somewhat justified.
The ability of a pope to resign was made official by Pope Boniface VIII who placed by decree into canon law:
- Our predecessor, Pope Celestine V, whilst he governed the Church, constituted and decreed that the Roman Pontiff can freely resign. Therefore lest it happen that this statute should in the course of time fall into oblivion, or that doubt upon the subject should lead to further disputes, We have determined with the counsel of our brethren that it be placed among other constitutions for a perpetual memory of the same.
If a pope wishes to resign today, there are official steps that can be taken. According to the 1983 Code of Canon Law (Canon 332.2), If it should so happen that the Roman Pontiff resigns his office, it is required for validity that he makes the resignation freely and that it be duly manifested, but not that it be accepted by anyone.
What this means is that a pope merely needs to make his desire to resign clearly known and that it cannot be due to outside pressure or fraud, but it isnt necessary that anyone accept his resignation. Ideally the resignation is given to the College of Cardinals, since they elected him in the first place and they can determine if the resignation is submitted freely. Regardless of whos around, though, once he does it, its finalized.