No I was not wearing headphones. I have a Rode Videomic Pro and after manually setting the mic to the correct volume I thought it was working. On a Canon 5D Mark II there is not a plug for headphones.
Ok thanks I didn’t think there was much hope of recovering it. This will never happen again, believe me. Here’s a pretty neat article on how some guys were able to extract sound from silent video https://people.csail.mit.edu/mrub/VisualMic/