The real unfortunate thing is no matter how hard to try to think of everything to avoid this type of situation, the tank always seems to find a way to show you yet another way to empty onto the floor that you didn't think about. This has been my experience with 4 floods, 3 on carpet, one on hardwood. I lost everything the first time because I was at work and the problem happened early in the morning, but the other 3 times I was home and lucky enough to have supplies on hand to save everything after my first hard lesson.
Still, if my power was to go out for more than 6 hours (that is how long my huge UPS will power my heater, powerheads, and return pump) then even on my current 75G tank I would have a small flood of about 5 gallons due to back syphoning/filling and overflowing my sump. I am kind of relying on me being able to get to the tank within 6 hours if that happens to avoid the problem because in the past I have relied on check valves only to have them all fail on me that the most important time.
Still, if my power was to go out for more than 6 hours (that is how long my huge UPS will power my heater, powerheads, and return pump) then even on my current 75G tank I would have a small flood of about 5 gallons due to back syphoning/filling and overflowing my sump. I am kind of relying on me being able to get to the tank within 6 hours if that happens to avoid the problem because in the past I have relied on check valves only to have them all fail on me that the most important time.