Can I get notified if an assets STOPS sending logs?

Yes.

If you don't recieved any logs from the IP address x.x.x.x in over 720 minute(s) this could be
an indication that the system is down and the following event will trigger:

TYPE = SYSLOG

"Client stopped sending logs"

You can also set a tripwire on this event and receive a SMS or email when this trips in the future by pressing the 'Save Filter' button and naming the query and choosing to send an event or SMS.