Kin is 100% not. Oda likes to drag out his deaths and make them dramatic, give a good farewell speech.
Not getting unceremoniously bonked in the head.
So, having said that, yes, Kiku and Kan could be dead, since they had a bit of a poetic speech before they went. Are they? Well, we’ve seen people survive far worse. There’s no difference between what happened to them and what happens to the combatants in every fight Zoro has ever had. And if that’s their death scene, it’s still a bit quick, not really like Oda.
The biggest chance for a death is if next chapter, Kine’mon gets up and gives his life to try and hold off Kaido.