User blog comment:Observer Supreme/918 Review and Thoughts/@comment-29325824-20180920134308

Personally, I don't think Momonosuke and co were the ones who faked their own deaths. My idea is that Kaido, after they escaped from him, claimed to Wano he had killed their entire ruling family to crush their hopes, uncluding digging empty graves to aid the lie.

Of course, the problem is letting the people of Wano know they're still alive without actually winding up in those graves.