A "Delay-OFF" relay module could provide some protection from an extended fluid-out condition. I've seen some that use FET switches instead of relays so they are smaller if space is an issue. 5V and 12V modules seem the most common, but as shown there are those with wider DC range for your 8V application.
There have been sporadic discussions on DIY fluid-out detectors such as sensing the resistance of the heater elements as a proxy for temperature but can be tricky to implement so that goes to how good of a friend are we talking about. 
I've pondered application of washing machine and vacuum cleaner sensors that sense the "dirtiness" of the flowing water or air to adjust operation. I figure such a mechanism could detect when the flowing air in the smoke stack becomes clear.
