Reminds me a popular movie...
Missing links in what? Are you talking about web links ? or you are talking about Unc address ?
If it is accessible using Unc path, connect to a service (say ping service) and try to get the response.
If you are talking about http path, you are just making one Web crawler. Same as the other, you need to request the link to get the response. If it is 200, Response is perfect, and you need to put the response to Cache. If it is 301, its removed permanently. 307 temporary redirection etc. (check status codes
And finally based on the response status, you update the database...