Failure at Marathon led the Persians to think that the only way tokeep things quiet was to bring the city-states in mainland Greecewithin their empire and establish an ethnic frontier, so theyinvaded peninsula Greece ten years later. If this had succeded, weshould remember that even under Persian rule, the Greek cities inAsia Minor prospered and maintained their identity, their culturaland scientific advances outpointing that of mainland Greece. Theysurvived there until 1923 CE when evacuated at the end of theTurkis-Greek war which continued on after World War 1.
And of course there were the western Greeks of Italy, Sicily andthe islands who would not have been under Persian rule.
It is interesting to note that more recenty mainland Greece spenthundreds of years under Ottoman Turk rule until it fought for andregained independence in 1832 CE. We just can’t know for sure, butthe Greeks were cultural survivors who would almost certainly havemade a comeback against the Persians, just as they did 2,000 yearslater against the Turks.