A few years ago, I was HJing a PTQ.

Antonio was playing his “I win” turn. He took a look at his hand, said “Huh? I am missing a card. Oh, ok, it's on the floor. Cast this, win”.
Nino raised his eyebrows, and called a judge.

What I did was the following:
I reconstructed, and made sure Antonio had the right number of cards (only five or six turns had passed, so this was at all possible).
Then I told Antonio: “Well, you are down a card, but we can't be sure the missing card is the one on the floor. Please shuffle this card into your deck, and draw another card”.

At the time, I felt like I had made a “creative ruling”… after reading the topic, I feel better.

Oh, and Antonio won anyway.