A possible scenario: All Supernovas are KOed, so as the Scabbards and BM and the rest of the enemies, the only ones who can barely fight are the SHs (minus Luffy and Zoro who are trying to recover after Marco healed them with at his limits) and Yamato, Kaido is nearly losing so the SHs and Yamato buys time and fight Kaido together a la Zombie Oars fight so that Luffy and Zoro can the finishing blow a la Morgan fight... Sounds cliche but possible I guess...