Permanently deleted files can never be recovered, so please be extremely careful when you use this feature.
Deleted and permanently deleted files do not count against your storage quota. Permanently deleting files after they have already been deleted will not free any more space in your Dropbox.
For Dropbox Basic (free) and Plus users, deleted files are permanently deleted after 30 days. If you have a Dropbox Professional or Business account, files are permanently deleted after 120 days. If you previously purchased the extended version history add-on to your Plus account, files are available for one full year.