User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-5938567-20130113181814/@comment-3146930-20130113195945

I actually think the most likely character to die in this series is Chiron. In The Lost Hero, he made it sound like he was ready to retire, and he is only immortal as long as he is needed. However, any character that was important in Percy Jackson and the Olympians are less likely to die because if anything happened to them, it would make any kind of character development they had seem completely worthless. It is why I don't think that Percy or Annabeth will die, because if they did then it would make it seem like the first series, every step that it took to get them to where they are now, would be kind of pointless as they will just die in the sequel.

While it isn't the same medium, it is like if a character that was important in Movie 1 dies in Movie 2, it is normally met with a lot of backlash. If PJ is Movie 1, and HoO is Movie 2, it would seem weird to have someone die in the sequel. It is more likely that characters would be phased out or have a minor role (which they kind of have been).

I admit that I could be wrong, but I just don't see them being killed off. However, The House of Hades is most likely when characters are going to start being killed (most likely).