Looking into the implementation of the local uploader, it also checks for file existence first and return `false` if the file to delete does not exist. However, I am with Jakob, that this is not really necessary. I'd suggest, that you change it in the S3 uploader and I change the behaviour in the local uploader. I will also update the documentation comment accordingly.
I'd say it should return `true` if the file is gone after the function returned regardless if it wasn't there in the first place.