Keynote files gone

Today I wanted to start my lessons and all keynote files for all subjects that I've been working on for ages and been using for ages are gone. I'm not talking about accidently deleting or unsaved files but real existing files that I've been using often. They're gone. All the pdf versions are still there in the folder but the keynotes (.key) are gone. Anyone who has a clue as to what could have happened and if there is a way to retrieve them (no they're not showing up in a finder search)

Thanks

Michiel