Indeed, happened to me on a ride with @HLaB. One of the cleats had come a bit loose and, as we dived into a bus shelter to escape a monsoon-style downpour, I found I couldn't unclip. Took my shoe off and left it on the pedal and HLab came to the rescue - either by knowing what to do or by guessing, he managed to get things sorted.
I now check the screws more often - well I now check the screws ...
I now check the screws more often - well I now check the screws ...