When I said, “The mind is forever released from the material body” That meant the mind (or more precisely citta) cannot arise after that.
The word “mind” has been used in English language as something that always exists. The problem arises when we try to find English words to match Pali words.
The following is a better description;
When a new bhava starts at a cuti-patisandhi moment, a hadaya vatthu for the new bhava is generated by kammic energy. That hadaya vatthu is where citta arise. But citta are not there all the time. For example when we are unconscious, there are no citta vithi, and the “mind” is in the bhavanga state.
– Even in between citta vithi (where thoughts arise), the “mind” is in the bhavanga state.
Therefore, what is absolutely correct say is that a new hadaya vatthu will not be created at the cuti-patisandhi moment for an Arahant, instead of saying “The mind is forever released from the material body”.
– There will be no new hadaya vatthu for an Arahant at death (i.e., at the cuti-patisandhi moment), so no citta can arise (and thus no mind to speak of).