The DIT has always taken my files at the end the day to download and to backup. But regardless, I always keep a back-up of my own. Not to use for later, but as safety and reference. I have had production companies call me up in panic because they cannot find certain audio files. This mostly happens because of mis-labeling. I would send them a file name for them to search, or just upload the files for them to download again. Problem solved.
Accidents happen and files do get lost. I always want to be able to offer those files to the production company again when that occurs. These audio files don't eat up my hard drive space so I don't mind keeping a backup archive.