User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-69.165.146.170-20121020153423

From Rick RIordan's Blog

The one thing I can promise regarding The House of Hades ***SPOILER ALERT****  At the end of Mark of Athena, Nico senses that Percy and Annabeth are still alive, despite the incredible danger they are in. Nico is right. They are alive. You WILL find out what is happening to them in the next book. They don't disappear from the story. **** END SPOILER ALERT*****