Pull the island into an alternate dimension. Then about a year later, have the island mysteriously reappear. When Diana flies back, we see the large grecian columns, the marble temples and walk ways. She lands to a greeting party all dressed in flowing togas and smiles. When she says the year was such a long time without them, they question her because they have been gone one thousand. In that time, they traded in their barbarism for peace and learning. Inventing and building until they had a machine to return them home.