The government has more recently come forth to pretty much recant that Nankai megaquake warning from a few days ago:
Naoshi Hirata, a professor emeritus at the University of Tokyo who chairs the JMA’s Nankai Trough earthquake assessment study group, said at a news conference on Aug. 9, “At this point, we have not obtained any data that indicates a change in plate movement that would trigger a Nankai Trough earthquake.”
https://www.asahi.com/ajw/articles/15384654
So probably no need to change your plans, (and with so many people now avoiding the area, you may now get a good deal along with a lack of crowds) but then again, there's still just as much of a chance of a massive Nankai earthquake happening as there was before, and its something they have been anticipating as an inevitability for years.