I see your point, however Johnny’s fight with Diego: The World only took 4 chapters, and I don’t foresee anything like that happening. When it comes down to Karera, I don’t think she’s coming back, and would be just like a side character from Diamond is Unbreakable, someone who would show up just for a small amount of time. As for Kaato, I believe she is being set up for a small arc to help flesh out her character, just like the maid Nijimura. I predict Jojolion ending in half a year, however everything in this comment is just speculation, and could be very wrong, especially given how unpredictable Jojo is.