If you have encrypted the USB drive with the key, which you have saved to the encrypted drive, and have subsequently have lost/deleted the key then there is no way of recovering the lost key.

However if you have enabled DESlock+ Go on the encrypted drive, then you could still access the drive if you can remember the DESlock+ Go password, by plugging the USB drive into a machine which doesn't have DESlock+ installed. You will then be able to copy the Key-File backup and restore your DESlock+ Key-File.

As a precautionary measure, we do advise that Key-File backups are taken and saved to at least two different locations, of which neither are encrypted.