Its very rare for a mining rig to burn a house down, especially end up killing someone while they sleep. You need to be reasonable.

I had tons and tons of rigs in the past, the most common type of fire failure was usually a melting PCIe connector, usually with modular PSUs. I checked the connectors from time to time, then got lazy and never checked and one day a GPU just kept crashing, after hours and hours of testing I discovered that a PCIe melted and it caused a bad connection which lead to the crashes. Another time a GPU fried and immediately the PSU shut off the rig since it detected a short. To my fault  I powered the rig back up and heard a loud BANG followed by a big cloud of smoke.

So as you can see, usually the rig will power off when there is an issue. And most people if not everybody due to fire codes needs a smoke detector in their place. So if a mining rig actually starts a fire, the smoke detector will wake you up and you can either put the  fire off yourself or just run outside.

But I agree with you, for little profit sometimes its best to just sell the GPU rather than deal with the headaches of when they crash in the middle of the night and you have to reboot them.