This is an area of planning known as "business continuity planning" and as part of this process, you should have a document and written procedures that are executed by humans, not computers, and tested as part of this. For example, your BCP should include people who are already trusted and know how your infrastructure works, and you should do a dress rehearsal on a yearly basis at least. A notification tool is one thing, but realistically this should be just one of your tools.