Have your MF system people set up auditing for the file. If you need to do it for security reasons, this is the only valid method, as all others can be bypassed by someone who is seriously motivated and has the knowledge.
If you just want to know if anybody needs that file, rename it and wait if someone calls (this is my method, really!)
If nobody calls for three months, move the file to tape archive.
Good news: We've extended SAS Hackathon registration until Sept. 12, so you still have time to be part of our biggest event yet – our five-year anniversary!