Most 3D printers don't have massive printing heads. If they drive into the end-stops, the motors will likely just skip steps and be stuck. They are not designed

Most 3D printers don't have massive printing heads. If they drive into the end-stops, the motors will likely just skip steps and be stuck. They are not designed to apply much force. I'm much more worried about the heating element. Its temperature is usually controlled by the same cpu that also does motion control and g-code parsing. If anything locks up the CPU the heat might not be turned off in time, and (because you also want fast startup) there is enough power available to melt something. At the very least you would get nasty fumes from over-heated plastics, and maybe even teflon tape, which often is part of the print head. At worst it could start a fire.