Contributed By: Brian Wren [MSFT]
The rules for firing alerts when a server is down are in the Consolidators PRG. There are 6 event rules that are right at the top of the list if you sort by name. These each generate a Warning which is not going to generate a Notification (e-mail). There is an alert rule that will send a notification if an alert of an Error or higher is generated. The easiest way to get the missed heartbeat rules to generate a notification is to change them from generating a Warning alert to generating an Error alert.