The First Work Of Western Literature
If you're going to lose anything, it might as well be a big one. That appears to be the reasoning that our species has used to the Margites, an ancient comedy epic authored by the Greek poet Homer, The First Work Of Western Literature.
Homer penned the Margites before the more renowned (and surviving) Iliad and Odyssey, according to various ancient sources. It was also reportedly quite good, with Aristotle asserting in On the Art of Poetry that it "essentially founded Greek comedy." And, given that the Iliad is now commonly referred to be the "first great book" and the "first work of Western literature," the glory should have gone to the lost Margites.
In other words, discovering this missing comedy would provide us with more than simply a new book by one of history's greatest authors. It would entail starting again with the whole Western canon. The Smithsonian named it the best work "you'll never get an opportunity to read" on their list of missing books, a fitting epitaph for Western Literature's very first item.