Earlier quoted context omitted.
Through a world wars I and II, the various rebellions and coups, a civil war? No, very likely someone would have 'harvested' them to sell for food. Come on! The Nazis systematically plundered art treasures across Europe. After the war much of that was lost. There is not really much doubt on this.
Half of the marbles from the Parthenon survive in the Acropolis Museum. In other words, the Greeks know what they're doing. The Elgin Marbles were taken when the country was owned by the Ottoman Empire. I really wish you would do some research before spouting off with ill-informed opinions. The Nazis and Italians conquered Greece during WW2, they didn't take Acropolis marbles.
Anyway, Elgin 'rescued' the marbles after a period of particularly egregious destruction of Greek history. Much was lost, blown up or deliberately demolished. If the Greeks didn't give a damn, why should Elgin be blamed for caring?