I saw the Jack Gilford Fledermaus back when I was still in college and I still remember his performance. I saw it in Cleveland; the Met was still touring then. But I've never seen a stage performance of The Merry Widow, only the Jeanette MacDonald movie (confession: I have never liked Maurice Chevalier, not in anything I've ever seen him do). Luckily, I missed the Lana Turner version. I don't think the original plot was used in either movie.
We'll just keep our fingers crossed for Kelli O'Hara.