A conscious Kaido with the ability to use Haki would have come out of this basically unscathed, considering the fact that he can envelop himself in special dragon flames that reach such high temperatures that they can vaporize things upon contact. There is indeed a reason why Oda chose to have Kaido revert to his "Base" form before falling into the magma, but that doesn't invalidate my argument. Kaido can literally emerge unharmed from an explosion of this level below.
The combination of Kaido's coating and scales is truly difficult to break through.
![](https://pbs.twimg.com/media/FUBMK_JUsAUYRJZ.png)
The combination of Kaido's coating and scales is truly difficult to break through.