We have some pretty good differential evidence suggesting that they would not have been destroyed in the Greek Revolution, if that's the specific threat you're

We have some pretty good differential evidence suggesting that they would not have been destroyed in the Greek Revolution, if that's the specific threat you're worried about. Elgin did not remove all the marbles, but only a portion, so we can easily see what happened to the ones left behind. He removed 1 of the 6 caryatids from the Erechtheion, for example; the 5 that remained in Greece are still extant. In addition, he removed about 80 meters of the Parthenon frieze; the 50 meters that were left are also still extant. These are all in the Acropolis Museum today. Oddly neither WW2 nor the Greek Civil War caused any significant damage either. The main damage that has taken place is post-WW2 due to the rise of car-driven air pollution, especially acid rain. To protect them, the remaining 5 caryatids were moved indoors in 1979 (replaced by replicas), and the last 20-meter segment of frieze remaining on the Parthenon was moved indoors in 1993. These would probably have been in better condition if they had been removed earlier.