They were going to escape. But in the end, it was Ace saving Luffy that made Luffy “fail" to save Ace. Akainu got under Ace's skin, and while Ace was down, Luffy dropped to his knees finally hitting his limit on another energy boost. And was distracted by Ace's vivre card that fell out of his hat.

Why no one saved ace?

One Piece Odyssey stays true to the manga, so players will not be able to save Ace in Marineford. One Piece Odyssey stays true to the manga and anime. This means it will not be possible for players to save Portgas D. Ace during the Marineford war.

Why couldn t Garp save Ace?

He doesn't want Ace to die, but knows Ace decided to become a Pirate on his own. He is a Marine, it's his life's duty to capture and kill Pirates. But Ace also died suddenly. There was nothing Garp could do to stop Akaino from killing Ace.