Hi there,
We recently had a report of quizzes mysteriously go missing as well.
Luckily, these were quizzes in which students already had attempted so I could track down the who and when by analysing the gradebook history tables.
After a quick review I did indeed find out what happened to the mysteriously vanishing quizzes! Professor Plum did it the Library with the Candlestick.
Turns out one of our prof's (who also reported the mysterious disappearance) forgot about a certain late night clean up he was doing in his Moodle course in which he also inadvertantly removed some quizzes.
Anyway, long story short ... you'll need someone with a bit of sql knowledge to do the query. Start with the gradebook history tables and you should be able to find out, at the very least, the date and time of the deleted quizzes as well as retreive any of the missing grades. And then you can go from there in terms of what might have happened at that time.