User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-3509916-20121101021154/@comment-3146930-20121101024039

I don't remember Mars telling Frank that Percy's choice would save/destroy the world. Only that it was a choice that Percy wouldn't be able to make without Frank's help:

"And someday soon, he’s going to face a sacrifice he can’t make. Without you, Frank—without your sense of duty—he’s going to fail. The whole war will go sideways, and Gaea will destroy our world."

Yes Gaea will destroy the world as a result of Percy being unable to sacrifice something, but Percy's choice won't directly cause the end of the world.