@comrade
Today's episode shows that Kaido remained immersed in flames identical to magma without suffering any harm. Even Gear 5, upon coming into contact with the temperature of these "flames," couldn't withstand it and quickly released Kaido, who was completely and casually enveloped in such temperature and remained unharmed throughout, not even being affected by the very "flames" resembling magma. It becomes increasingly difficult to say that Kaido is really dead when, in his final moments, he was able to achieve such a feat. The guy was technically, in a rough sense, covered in magma and somehow died from the magma? LOL
The only real possibility for Kaido being killed is because he is seen knocked out in his basic form, which is the least durable of the three forms he possesses. However, even in his basic form, as demonstrated in Kuri, Kaido is still durable. It's a strange decision considering that characters like Lucci and Kaku, even after being defeated, remained in their hybrid forms (I think the Beast Pirates also did the same).