I can't figure it out... at first I thought it was some secret bears thing, but maybe it's to represent a vacant papacy while the conclave (possibly player included) debates the successor?
That's right: If the pope dies, the Holy See itself will take over and the cardinals will come together to elect a new Pope through an event chain. Originally, I wanted to make use of the new elective succession for this, but (a) there's no reliable way to know when all electors have voted and (b) I think it doesn't really fit: The votes should be secret and there should be multiple rounds of election until someone gets a majority. So I've scripted the whole election stuff using events: First, each Cardinal can decide whether he wants to attend the conclave (if they can attend - being imprisoned prevents you from going to Rome; the ai will always try to come). After a few days, there'll be the first election, where the player can use a targetted decision to cast his vote and the ai picks the best candidate in it's opinion (himself, their family, someone they like (friends and in case there are homosexual cardinals, lovers), characters of their own culture, etc.). If someone get's a majority, he will become the next Pope, otherwise there will be a new election round a few weeks later. Also there's a chance for a Cardinal who didn't get very many votes to say that he doesn't want to get any votes anymore (guaranteeing that eventually, the college will elect someone).
Speaking of the time it takes to elect a new Pope: Since most of the time it takes many rounds of election, it can take a while. The time in between elections is quite long, so the whole process will be very slow. If however, the election should take unusually long, an event might fire where the cardinals will be locked in a room. From this day on, the cardinals get penalties (bad events) for being in the conclave, therefore the time in between elections will be much shorter.
Oh, regarding papal infallibility: Now, there's a small chance for an event to fire when the college declined the appointment of a new cardinal, in which the Pope will think about why his infallibility. Chairs might be involved...