If you are within 90 days of the end of your cruise, you can sign into the Disney Cruise website, go to the "Already Booked" menu, select "Castaway Club" and scroll down to My Cruises. You should then see your past cruises and be able to select the folio.
You can try looking at your cruises on the Castaway Club page if it is a recent cruise. If it isn't there, I don't think it can be recovered but you could try contacting DCL.
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