How to know when a cluster node goes offline

I have a plugin that keeps track of particular logins of a particular user. This user logs in multiple times as different resources to different nodes in a cluster. I can easily track when the user comes online and offline. However, if a cluster node dies and/or is shutdown, how could I catch that event so I know that user is no longer online? Normal presence packets don't seem to be sent out in this case. Is there a hook that will allow me to track node outages. This would be useful for self monitoring too of a cluster.