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.
-snip-
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.
It maybe safe in the 1st world fire-alam ridden countries you live in, but in different part of the world, houses and homes rarely have fire any alarms. What exists in these parts of the world are fire hydrants at the most (probably because fire alarms add up to additional electricity costs). So the threat of fire from mining rigs is a real thing.
I also agree that mining rigs are better off sold if the profit is too low. Don't just count on the calculators to project monthly profit it's important to consider down-time, freezes, and restarts that use up electricity even when not mining.