Expats expect to come home at some point in their lives. Emigrants (the word I think you were looking for) leave for good.
https://english.stackexchange.com/questions/97835/difference...
https://english.stackexchange.com/questions/97835/difference...
Emigrants leave and immigrants come. It's two sides of the same coin. You can't emigrate without immigrating. Except if you manage to become stateless and remain on international territory.
Migrants is just the term without the direction. Which is unnecessary if you're not talking about the country they leave or move to.