There really isn't anything that does this because LANDesk doesn't send any kind of event when a machine goes offline. This is why we created Power State Notifier as it automatically updates the machine's inventory record when the machine state changes such as on/off/standby, logged in/out and screensaver active.
Take a look. It's a free plug-in.
Mark Star - MarXtar LANDesk Enhancements
Home of Power State Notifier & Wake-On-WAN for LANDesk