If the nectar-flow at the apex of the KuNDalinI yoga could only cause the non-decay of the body and nothing more, I am sure real yogis would not have gone the path of the kuNDalinI yoga. After all they were after an eternal bliss, not an eternal body.
The flow of amRit from the thousand petalled lotus seat in the sahasrAra-chakra is just a step prior to the Realisation of advaita. In addition to that it certainly can give to the body, so long as it lasts, an enviable health. But it is mainly intended to shower the divine unlimited bliss.