How long did Greek last in various colonies

Factual Questions
1

The Ancient Greeks sure got around and there were Greek settlements from Spain all the way to what is now India. In many of these places, Greek would be the language. Today of course, almost all of them speak different languages and for many they had different language from Greece preceding the present tongue. My question is when did Greek die out in various places?

At least one book claims that their is evidence that Greek was still spoken in what is now Gujarat in Central Inda as late as the first century after Christ (its at page 321). If Greek could survive for so long in a place which was so far away, it makes me wonder how long it survived nearer home. I know it was the language of the Eastern part of the Roman empire, but when could you gave spoken Greek in the South of France and been understood?

2

Google “Griko” for articles on a Greek dialect of southern Italy
still spoken by perhaps 80,000 people, although not necessarily
as their first language.

Opinion is divided on their origins. They may have originated
as colonists during the ancient colonization era, or during the
Roman era as poor immigrants, or during the early Byzantine
occupation of the area, or as refugees from the Turks toward
the end of the Byzantine Empire. Some combination of the above
is also possible.