Once the file is accessible by one, they can put it on a flash drive for example and share it through out the company.

As to the server fail, or data erased, that's why we keep backup copies.
As to the internet, if you put it on the cloud, it's out there for most governments and the cloud company to share so that defeats again you locking the files down.

Until you accept that access = possible leak, you will keep searching.
Bob