Have a plan, at least a generic outline of what you will do under given circumstances. It's a subset of what management should have in place for their business continuity plan. Management has one right? So should you.

Consider in advance the steps you would run through, the checks you would make and why you would make them. The plan may help yourself and others really understand the purpose of the data housed on server A and who consumes it. Having a list of data consumers is the starting point for that notification list of business people who need to be in the loop when disaster strikes.