Good to see that you are still lurking around :D
The archaeological evidence suggests that the island of Santorini was likely abandoned before the Bronze Age eruption of Thera. It is likely that there were many precursors to the eruption, which caused the popular ion to sensibly flee. There is some evidence to suggest that it may have been in a hurry, but that it appears that there was intention to return. I have no idea whether the population did return straight away (there was probably little to return to), but there appears to have been a population living on the island from the 9th century BC, so that is probably what is being referred to in Edith Hill's book.
Thera is rather topical at the moment, as I will soon be submitting a paper regarding the eruption. Watch this space for an update (assuming it is accepted!).... and other, far more interesting news (at least it is far more interesting to me).