You can probably get another King if he died, but I think either you don't get another Baron or it's bugged at present.
I've also had one or two zombie sieges, but I don't think those are really plausible for a starting to intermediate player to fight against and win. Zombies might not be the impossible to kill demigods that they were before, but I don't think they're really balanced yet.
While I'm asking, what are the limits on invaders being able to climb walls now? is it only 1 z-level high walls that they can climb, or am I still not safe if I have a wall with an overhanging fortification on it?
Zombies, as a newer player (though learning fast), are a pain in the ass because of the sheer amount of them and how easily they kill people. Making a dropping tunnel was really the only way I could deal with them.
And invaders can climb anything that doesn't have a roof above it (they won't hang upside-down), I believe. I had a zombie climbing around like a bastard in my drop tunnel for several months, on SMOOTHED WALLS. He did not care.