User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-74.103.167.208-20130311191323/@comment-5774152-20130321035612

I don't think Hazel could bring Nico back. You have to remember that Nico is more about controlling dead people, where Hazel is more about gems and underground things (Nico does underground things too it's just-oh nevermind that doesn't really matter here). I really don't think she would have the kind of power.

Even if she could, she would have to take someone's life to bring him back anyway. Remember The Battle of the Labyrinth when Percy was freaking out because he thought his life was the one Nico wanted to take, when really he was going for Daedalus. Then after Daedalus sacraficed himself to bring down the Labyrinth, Nico used his soul to try and bring back Bianca, but she chose to get reborn, so he brought back Hazel instead. So it's not like children of Hades just bring back dead people when they want to. There's a whole process involved, soul for a soul.