Who lives where?

Maybe "down on their luck" would read better as stuck in a poverty cycle.

Probably a more complex question than meets the eye due to the fact of family 'values' and how they percieve they should live together, i.e never leaving home. Unless you are female and marry, then you get live at your husbands extended families home....

The major tourist areas are in the North of the island,  along the West Coast and in some spots on the East coast.

The main tourist areas are also where most expats live.
Towns with the highest concentration of expats are Grand Bay, Pointe aux Cannoniers, Pereybere, Mon Choisy, etc in the North; mainly European and Russian expats.
The West coast towns of Flic en Flac and Tamarin have large South African expat communities.
Quatres Bornes and Ebene in the center of the island house large Indian expat circles.
Port Louis, the capital has a large Chinese expat community but also very diverse.

Outside of the tourist areas and the aforementioned names, you are less likely to meet an expat.
The districts of Savanne and Grand Port, both in the South, have the smallest expat populations.

There are communities, gated or not, where wealthier locals live...as is the case in most countries.

Going by the exact definition of the word, there are no slums in Mauritius. What you can see are pockets of underprivileged families here and there who occupy state land illegally thus lacking basic utilities and comfort.

Very informative succinct post WinstonH which answers the question perfectly.