I do see him exchanging Sandai for the Nidai. A cursed sword for another cursed sword. We might also get another moment of Zoro overcoming a curse. I don't see the Sandai breaking tho, if a scratch on a sword is a swordsman shame, then I can't imagine how having a broken sword would affect Zoro's reputation. Maybe the citizens of Wano after realizing that Zoro has a cursed sword, they might want to give him Nidai thinking that since he tamed both Sandai and Enma, taming the Nidai should also be child's play. And also as a thanks for saving their country lol.