Really. It's best not to trust on shutdown procedures for fail-safe persistence if that really is important. Use log-structured file-system and do cleanup and verification when the power is restored. When microcontrollers have brownouts, it's best to assume that you may have already garbage in the memory bus.

Of course, when improved fail-safety exist just to improve reliability measured in hours and fail-safety is not critical function, all what I said is irrelevant.