Except that the Library of Alexandria was never under any siege... 
I think a lot of people would be bitterly disappointed about a lot of the contents of this and other ancient libraries that were eventually lost. Lots of commentaries on Homer by hellenistic Beckmessers and Headmasters and books on magic and divination.
And, sure, maybe some lost Sophocles tragedies or Democritus or the 2nd book of Aristotle's Poetics
