In Dzogchen there is a phenomenon called "rainbow body."
Here is some context: "The ultimate fruition of the thodgal [meditation] practices is a body of pure light, called a rainbow body [...] at death, from the point of view of an external observer, the following happens: the corpse does not start to decompose, but starts to shrink until it disappears. Usually fingernails, toenails and hair are left behind."
Here is how I think this happens: advanced meditator consciously de-couples the bonds between hydrogen and oxygen (which coupled constitute 70-80% of water contained in our bodies). Put differently, the mostly water-based human body simply evaporates as these two elements return to their gaseous forms.
Rainbow body phenomenon is an extreme form of letting go, a detachment so profound and system-wide that it plays out at a molecular level.