Annabeth has died from Calypso's curse in Tartarus. When Leo returns with Calypso. War is over, when Gaea taunted Percy about Annabeth and he created a hurricane that lifted her off the ground just in time for a giant Leo-fireball to kill her.
Third POV
"Rooooaaar!!!!!"
A giant metal dragon descended from the air above. Curious campers came crashing out of cabins.
" Yeah!! Leo Flamin' Valdez is back!!!!"
At these words the five rushed out of their cabins, none as fast as Piper, whom longed to see her best friend besides Jason, and Percy, whom was overjoyed of having a day where the guilt was not so overpowering with another friend safe and not dead because of Percy.
The dragon landed in the middle of the arena settling down with a thump. There on its back was a Latino elf and a girl with caramel hair. They leapt off and at once Leo was swarmed with hugs and a slap, courtesy of Piper.
"Oh, and umm this is...,"but he trailed off looking at the girl and Percy, who had a grief-stricken face.
"You"
"Percy! So nice to see you again! How's Annabeth?"
"Dead"
"Oh I'm so sorry. How did sh..."
"Why Calypso" His harsh tone scared every single person listening, even Nico.
"Why what?"
"Why didn't you curse me? YOU SHOULD HAVE CURSED ME! IT SHOULD HAVE BEEN ME! DO YOU EVEN KNOW WHAT IT COST ANNABETH, COST ME???" He sank to his knees sobbing, begging her to place the worst curse she could think of on him and send him back to Tartarus where he belonged.
Everyone was shaken, and Calypso realised the full weight of what she did.
" You should of left me on that island, Leo"