Sonix saves deleted files in a "trash can" on your home screen. Deleted files are stored for 7 days so you can restore them if desired. After 7 days, the deleted files are marked for permanent deletion and are then purged from our storage servers. 

If you want to permanently delete a file immediately, you can do that by clicking the "delete permanently" option.

Once a file has been permanently deleted, there is NO WAY for Sonix to recover or restore your files. They are completely destroyed.