Hmmm. I managed somehow to screw up the "character_health" file, so no characters anywhere in the world died of natural causes. I thought my king was just unusually long-lived (he was 69) but then I noticed a courtier in another court who was 115...
I fixed it by over-writing the file with a clean copy, and my king died shortly thereafter. My heir (who had his own county) had died somehow- I imagine in battle- so his son took over. He was 8 years old.
He was later assassinated (one of those "your bedroom door opens suddenly" events) by, I assume, a rebellious vassal. I am going to have to see how that happened- it had never happened before to me before, so either the fact that the ruler was a child or that he had fairly low prestige must have increased the odds.
All of which is a long way of saying that I suppose a vampire king could be assassinated or else die in battle.
I was pondering how one could use existing traits and attributes to model the effects of vampirism. For instance, a discovered vampire might gain the kinslayer trait to reflect his horrible unpopularity. A vampire might default to getting the severely wounded trait so as to explain why he does not lead the troops (he has to stay out of the sunlight). Perhaps one with really high intrigue might be able to "recover". Or if he ceases to be a ruler (by having his lands conquered or something). This would be an AI character, but these former kings might go on to other courts. It would be best that they lose kinslayer and severely wounded traits if they cease to be rulers.
I was thinking of modifying the various illness and death events so as to create a huge modifier for high health. Give a MTTH for death by old age a factor of 10000 or so for a health of 20 or higher. A vampire, of course, could be given a +20 or so to health when it is created (and a penalty to fertility).
The idea is that instead of having to modify scores of events to incorporate vampires (chances of realm duress, courtier disloyalty, etc., etc.) you could use existing traits to do most of the work for you.
It would introduce a few quirks, of course. If, somehow, a regular character got a health of 20 he or she would not die of natural causes. But that is a feature, not a bug. I think it would be neat if a few folks were naturally immortal. Kind of like the legend of the wandering Jew.
And if we used kinslayer + severely wounded to represent a known vampire, then some characters would acquire these traits naturally. I'm inclined to include an event that gives these guys a boost to their health so they actually do become vampires. Other events would enable them to pass the trait on to their relatives and/or courtiers.
So, in summary, I was toying with the idea of using the following instead of the user defined traits:
high health (20+) = vampire
severely wounded = ruler vampire
kinslayer = known vampire
Modify the factors for high health to give a truly ridiculous bonus to the MTTH for the health events. Enough that instead of dying in a few days after reaching age 80, you will last for hundreds of years. And ensure that you recover in a day or two after getting illness, plague or pneumonia. But you never recover from being severely wounded.
The severely wounded is to explain why the vampire king is rarely seen, and never leads his troops. I am assuming that vulnerability to sunlight and being unable to cross running water is incompatible with leading troops. Besides, there's the risk of dying in battle which is best avoided.
Kinslayer both represents a way of becoming a vampire (if there's an event that gives high health to a bedridden kinslayer) and shows the social stigma of being a known monster. Heretic might work too/instead. Especially if a heretic king has a chance of passing his heresy on to others. Dunno.
p.s.
Maybe turn fosterlings into vampires? And find a way of making them stay (the DVIP has an event that makes fosterlings return home). Or else add bastards periodically. The text for the event can be that they are babies stolen from their mothers, or something.
The event to make courtiers into vampires should be triggered by their high ability scores. Maybe it already is- I should look at the event again.