Defined as “Does cryonics preserve cellular structure and brain pattern?” the answer is “yes.” Defined as “Do we have cryonics patients who have been resuscitated?” the answer is “not yet. However, there are multiple proofs of concept. Cryopreserved humans who were “frozen” as eggs are walking the planet, literally thousands of them.
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.