Two multi-headed Snakes that can survive decapitations and possibly even worse and that require intelligence and an absurd amount of punishement to be put down for good. The forms may be different but it's nearly the same.
I do not think that Orochi is dead, and even if it wasn't his df I still think that Kanjuro could have possibly saved him with his df.
Orochi's death would have felt more permanent if Big Mom had just took his soul instead of Kaido beheading him since his DF is the Yamato no Orochi. Given what that mythical creature is capable of doing, there's a chance that Orochi is still alive.