It’s a critical health code violation to take the served food back into the kitchen, let alone serve it to another customer. Not that it DOESN’T happen, but it is unlikely.
I know it happens because I worked at Walmart and many of my coworkers would routinly put returned food back on the shelves from the go back bins when they were supposed to be trashed, because nobody ever wanted to do the trash process or even was told about it (I only knew how and that it was a thing because I would constantly waste time going on the company intraweb and doing lessons on all the positions in the store instead of working).