I know this could go in the DF questions thread, but it's not a 'I need help with ___' kind of question and is more of something to think about.
A bit of a backstory here, I'm looking at the legends and stuff to try and help decide between two possible worldgen sites that the ultra sitefinder found. So, I looked at the civilization nearest my embark site for the worldgen I'm looking at which happens to be a pretty huge civilization, especially considering the fact that the worldgen has only gone for 300 years. I was looking at it as I was just curious (aren't we all?) and I was a bit confused when there wasn't a king for a long time. In fact, the current king became king in 218 and he was born in 181. It is now 302 I believe since I made a temporary crap fortress as I was trying to figure out something with visual fortress. So, that means he is 121 at this time. Dwarves generally live 150-170 years (I've heard a few people say that some dwarves lived longer than that, but there are RL people who have lived for over a century, so it's plausible), so I'm not afraid that he will conk out on me from old age. However, this brought up a thought, what if the regent (king/queen) was very old (I don't think they retire due to old age, yet) and they died of old age before appearing at your fortress.
I know that if they die at your fortress, they don't get replaced. Liasons don't get replaced I think, but the details on this aren't clear on this since they only appear in worldgen, BUT the world still changes even while you're in fortress mode and that makes me think, wouldn't the king's/queen's successor take their place when they die?
While the wiki says they won't get replaced, it conflicts with what some people have said.