According to the Wikipedia, “Apostasy (Greek: apostasia ’a defection or revolt’) is the formal disaffiliation from or abandonment or renunciation of a religion by a person. One who commits apostasy (or who apostatizes) is known as an apostate. The term apostasy is used by sociologist to mean renunciation and criticism of, or opposition to, a person’s former religion, in a technical sense and without pejorative connotation.” The Wikipedia discuses apostasy as viewed by several religions but not by Buddhism. I think one can legitimately raise the question as to how Buddhism (or Buddhists) would view someone who has abandoned Buddhism. It seems in general no follower of a religion or ideology would endorse or encourage another person to renounce or abandon the religion or ideology that one follows. A Buddhist would perhaps also never happily endorse or encourage a fellow Buddhist to renounce Buddhist teachings. This is because the teaching of the Buddha is often seen as a cure against all saṃsāric ills. Endorsing or encouraging others to give up Buddhism would be like endorsing or encouraging a patient to give up medicine. But should a patient choose to renounce the life-saving medicine, one cannot do anything. What one can do at the most is be compassionate to the patient and wish him/her well. Exacting death penalty or other forms of punishment or persecution from an apostate of Buddhism would be like executing or torturing a patient because he/she has refused to take medicine. Such a Buddhist attitude towards apostates of Buddhism would only make sense only in the light of the Buddhist notion of what Srinivasan once called “salvific privatism” (Heilsprivatismus). That is, salvific mechanism functions according to a certain law of nature, and one is solely responsible for detangling oneself from one’s own saṃsāric bondage. If one slanders the Buddha, Dharma, and Saṃgha, one does so at one’s own risk. If one respects the Buddha, Dharma, and Saṃgha, one does so for one’s own good.

Philosophia Buddhica