I actually know more than one person who did this or their parents did this. The made it work because they all basically retired early (e.g. late 40s, early 50s) using the strength of their US/European currency versus the currency in their home country. Basically, they spent 15-20 years working and then went back and became teachers. None of them moved to the relatively HCOL areas in their home countries though - more to 2nd or 3rd tier cities or more rural areas.

First thing they did was purchase a home, car, furniture, and that took care of the typical monthly expenses that eat into your salary. The rest went into CDs or other fixed income accounts. If you combine that with a teacher's salary, it's more than enough to live a basic and comfortable life.

I think the only caveat here is currency value fluctuation. The laws and rules about how you keep your money in accounts (e.g. American Dollar versus local currency) can vary a lot and change over time. The weakening of a currency can basically force you to change your plans. Some people have to "unretire" after a while.

None of the people I'm thinking about were "rich" by Western standards when when they lived in US/Europe. So it's not a story of some startup millionaires who went back and lived a life of luxury.