That often is not a server question, but an application access question. As an example if we lose a dns server, the other servers are not down you just lose the ability to create new sessions. The research is much like the Y2K studies that had to be done over a decade ago. What applications are on which servers and how do they interact. You'd be better off creating a drawing that shows application interactions (who needs dns, who needs sql, who needs sharepoint (and what does it require) as your starting point.
I think 'asset gen' has a services component to show application availability.
al