I would assume the file went one of two places, either to the filemaker go documents folder, or more likely, where audio files usually go in iOS, into iTunes. Check iTunes for your audio file.
As for dropboxing of files, the only way I've done that successfully from Go is to have a robot machine running that can export the file to a dropbox folder on a pc or mac running FMP. That requires sending the container to a served fm file, then sending a command to the robot specifying the record to pull. It does work, but it's a bit kludgy.
iOS8 had some improvements that allows apps to offer their service via the native iOS dialogs, I haven't played around with dropbox yet but I'd assume they would eventually have the ability to "save to dropbox" directly from any native iOS "save as" dialog.
An export can only go to the temp folder or documents folder. What path did you set in the script? After exporting , go back to home and select Device. The exported file should be in the list of files.
Empty export files will be automatically deleted no matter the location. I assume your file is empty, if it is not in either the temp folder or document folder.