Let me offer an alternate structure.
Trigger off any Thing status change.
Cancel any existing timer, regardless.
Examine the new status.
If it is OFFLINE, then set up a Timer to send an email in future. (No need to check status here.)
Note that if a sick Thing keeps bouncing on and off quicker than your timer, you’ll never get an email. Whether that can happen depends on the mystery Thing. Thing status is not a reliable guide to real availability, nor is it intended to be.