The delete happened on and it is now and we are no closer to having anything happen. They checked the delete files and Rewind and came to the conclusion they would have to carry out a Rollback to a date/time before the date/time of the deletion event because the usual methods of recovering files (Undelete and Rewind) could not be used. They needed access to my computer so they could use a pointer on the screen, allowing me to navigate the Dropbox App while they watched. I contacted Dropbox to see how I could get this resolved. As the contractor wasn't an Admin their account did not have permissions to delete any top-level folders, so it looks like this is a security issue with the Dropbox application. When the contractor booted up their computer with the new HHD installed, Dropbox deleted all the top-level folders the contractor was a member of. This came about because one of our contractors, who had the Dropbox App installed on their computer, decided to update their hard disk drive by using a disk imaging App. This has basically put us out of business until the issue is resolved. We have had a large number of folders/files deleted on our Dropbox for Business but Undelete only partially worked and Rewind didn't work at all, so we cannot access thousands of files which have disappeared.

Dropbox restore deleted files