u/KRT10N

We know that Whitebeard never expected to leave Marineford alive, but he was confident that he would be able to save Ace, even before Luffy's arrival on the battlefield. The issue is, Ace was chained up to the execution stand and Luffy got the key from Hancock, who wouldn't give it to anyone else, and from Galdino, who was in Impel Down.

Did he plan to break Ace's chains with Haki like Rayleigh did in Sabaody? This would require him to make it there, and honestly, I don't think he could.