Cryonics "Works" if this is defined as "Preserves tissue and structure with high fidelity. As of 2017, Cryonics does not work if this is defined as "Bringing back humans or animals from liquid nitrogen temperatures." As a relevant point, Cryonics works remarkably well in preserving structure compared to any alternatives.
If the power goes out at the cryonics facility there are protections to prevent you from unfreezing. The liquid nitrogen in the cryonics container (known as a Dewar) is not powered by electricity. The patients remain at -196 degrees centigrade as a natural function of liquid nitrogen.