Ouch... Sorry to hear about that, Susan. That sort of thing has always terrorized me. I've spent a fortune on automated power backup and redundant heating and cooling systems around here. The first thing everyone needs to learn and keep close to heart is to NEVER, EVER trust a single thermostat to control heat or cooling. I have heard countless tales of people losing everything when a single thermostat would fail on them. If you are wiring up your own heating/cooling system, it is very little extra trouble to wire in two thermostats rather than just a single one. And that little extra step could save your bacon one day.
Which also means, in the summer, never rely on a single air conditioning unit to keep a room or building survivable in the heat of the day.
If ever there is a favorite playground for Murphy's Law, this most certainly is it.