According to the search results, Kaido and Big Mom were defeated during the events of the Wano arc in One Piece. During the fight, Luffy sent Kaido crashing from Onigashima into the underground of Wano with his strongest attack, called Bajrang gun, and both Kaido and Big Mom were seen having landed in a pool of magma under the Wano Country. As One Piece Chapter 1050 announced Luffys victory, fans saw the very volcano in which Big Mom and Kaido landed erupt. The two likely flew out of Wano Country as the eruption was one of a grand scale and even clouded the skies above the country. However, their fate remains up in the air at the moment, and it is unclear whether they are dead or alive. Some fans speculate that they are alive but in a very bad physical condition. Others believe that they are dead, and their devil fruits will return to the wild. In Road to Laugh Tale vol. 2, it is confirmed that both Kaido and Big Mom have been defeated and will not be coming back, which suggests that they are dead. However, it is important to note that Oda avoids killing off characters as much as possible, and the criteria for determining whether a character is dead or not is ambiguous.