Most freezers have a "fast freeze" setting, this bypasses the thermostat and runs the compresor continualy, thus cooling the freezer to a lower temperature than normal.

If a power failure is expected, then useing the fast freeze setting before hand will extend the holding time.

Whilst some power failures are random, many result from bad weather, wildfires and industrial disputes.
In such circumstances use of the fast freez setting in advance would help.

Food which is defrosted but still cold should be safe to eat if cooked promptly, but most would advise against re freezing.

For homes that are regulary left unattended it might be prudent to place in the freezer a thermometer that records the MAXIMUM temperature reached.
This would warn the owner if the freezer had defrosted and refrozen whilst they were away.