It's not the first time a public playlist is deleted or changed, and unfortunately there's no way to recover it if you're not the owner.
To me, it's considered good practice adding to your library (or saving into a private playlist) music you like from public playlists. That way you can customize it to your own liking.
Also, opening a last.fm account is a great way to keep track of what you listen in Spotify, and most other music players. You just need to add your last.fm account info in the Spotify preferences, and it will log what you listen to. With this, you'll be able to see what you were listening at any point in time. Very useful!
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Note: I'm not a Spotify employee.