The body dies normally; the mind enters parinibbana, ending all rebirth and mental activity permanently.
Nibbana (or nirvana in Sanskrit) is not a place or afterlife destination. It is the permanent cessation of craving, aversion, and delusion—the three roots of suffering. When someone attains nibbana while alive, they experience profound peace and freedom from mental affliction. However, they still inhabit a living body subject to normal physical processes.
The Buddha explicitly taught that nibbana is "the unconditioned," existing beyond the cycle of conditioned phenomena (birth, aging, sickness, death). It is not creation or annihilation but rather the end of the restless movement that characterizes unenlightened existence.
The body of an enlightened person (arahant) decays and dies like any other body. There is nothing physically different about it. The Buddha's own body was cremated after his death, and the remains were distributed and enshrined in stupas, following normal practices of the time.
The difference lies entirely in the mind, not the flesh. An arahant's body is subject to the same natural laws as anyone else's, experiencing illness and aging. What is gone is the psychological reactivity—the person no longer generates new karma through craving or aversion.
When an arahant dies, they enter parinibbana (literally "final nibbana"), which is distinguished from nibbana attained while living. The Pali Canon describes this as the permanent extinguishing of consciousness and all mental formations. The five aggregates that constitute a person—form, feeling, perception, mental formations, and consciousness—completely cease.
This is not sleep or unconsciousness in the ordinary sense. According to the suttas, parinibbana is not a state of experience at all, because there is no experiencing subject present. The Buddha refused to characterize it in positive terms, instructing his followers that it cannot be adequately described through language tied to conditioned experience.
A fundamental point: there is no rebirth after parinibbana. The arahant does not go anywhere, encounter anything, or experience any consequence. The cycle of rebirth driven by craving and karma ends completely.
The Buddha taught that without craving, there is no linking of consciousness to a new life. Since the arahant has eliminated craving entirely, the mechanism of rebirth cannot operate. This is why enlightenment is described as escape from samsara (the cycle of rebirth), not as entry into another realm.
Theravada Buddhism, which closely follows the earliest texts, maintains that parinibbana is the complete cessation of all experience and mental activity. Mahayana traditions sometimes describe Buddha-nature or a subtle consciousness that persists, but this represents significant philosophical development beyond the earliest teachings.
Most traditions agree on the essential point: an arahant's death brings the permanent end of suffering and the impossibility of further rebirth. The practical and spiritual significance—liberation achieved—is consistent across schools, even where metaphysical interpretations differ.
The Buddha famously discouraged excessive metaphysical speculation about post-mortem states, calling such questions "undeclared" and not conducive to liberation. His focus was always on the present reality: understanding suffering, its causes, and how to end it through ethical conduct and mental training.
What matters practically is that enlightenment, whether achieved before or after death, ends the painful cycle of craving and rebirth. The details of what happens in parinibbana are less important than understanding that it represents complete peace—a permanent end to the struggle that characterizes ordinary existence.