The game will have a number (currently unknown) of regions that constitute "session instances", but in addition to not knowing how many there will be at launch, we also don't know what they will be.
The only region we've seen was from the E3 (and subsequent) gameplay demos, which is the Quirimbas Archipelago off the coast of Mozambique.
Will one of the regions feature the coast of Madagascar? Mauritius and Réunion? Maybe, but unfortunately we just don't know yet (as with so many things). I could speculate about where I think the game's regions will be at launch, but that would just be guessing at this point.