Can you please clarify - are you talking about the moment before you interact with Vestia at the center of Sablee (in front of the blue seal)? If yes - you won't be able to return to Sablee once you progress to the next area, so 100% every available location before that.
UPD: And that is the same for other areas you will go through. See a warning with confirmation? - Better go back and clear everything.