Board Thread:General Discussion/@comment-33722574-20180410015132/@comment-25536775-20180415220226

Any of them could've died and "not made a difference", since the plot would've been reworked to allow for the Seven to succeed anyway. But assuming no major plot changes (and this is going to upset a lot of people), Annebth could've died at any point after the Mark of Athena and the plot would've suffered very little. That was her central book and she was peripheral after that. Leo's "death" at the end of the Blood of Olympus could also easily have been made final (and it would've made for a better storyline). Hazel and Frank were also sidelined after the House of Hades (Which I'll never forgive Riordan for), so they might fit too.

It depends on what point in the story they'd die.