We get it fixed - somehow - immediately. Not always easy, and usually quite stressful. But we somehow pull it off, even if it means working late.
But also, we regularly perform checks of everything between each guest. Water, electricity, heating and cooling, insects, appliances, etc.... We often find potential problems that way, and try to resolve it before it becomes an imminent problem. Sometimes it might mean buying a new appliance (right now - today) rather than calling someone out to fix it, then getting the nonworking unit fixed in the mean time and if fixable, either sell it or use it as a "backup".
In any case, I'd much rather go through the stress than cancel a booking at the last minute, leaving the guest to figure out what to do next - and not to mention Airbnb penalties for that.