It can happen. I was once at the gate when my ELP-ATL flight took an hour delay. The pilot got on the PA and explained we needed a part which could come in from SLC but because of logistics it would necessitate cancellation of the flight. We were all sent back to the counter for rebooking.

About 30 minutes later the captain came to the counter, stopped the rebooking, got on the PA and announced they found a part right there in ELP and AA was going to loan it pending replacement the next day from DL inventory.

Thus the flight was reinstated, everyone sent back to the gate, and after an hour or so to complete the part replacement and apparently extensive FAA part tracing documentation, we departed.