Nah, Hyou dying only is not enough to call it tragedy, It's not like he isn't a likeable character but it's not enough. Showing people dying from a island falling into them is what i would call a tragedy. And of course showing the loses in our side after that would be a lot better.
Kaidou falling already? I doubt that, first of all we don't have all the matches yet(Sanji is the example to this), we don't know anything about Fukurokuju, Hawkins, Sanji's match, the person who we suppose could be Hiyori, Yamato and Kaidou's backstory, the person who was talking with Marco in Nekomamushi's ship, etc. And Onigashima is moving at a high speed and is already near the flower capital but you think that the last boss of this arc will fall already? How?
If Oda didn't plan Onigashima to fall into the flower capital then he wouldn't show us Mt Fuji this soon because it wasn't even necessary. It's impossible to defeat Kaidou in just a few chapters.