1. Dipo’s question: “Also, is there ever an event where a gandhabba is completely annihilated, such as in a parinibbana of a Buddha?”
– It depends on what you mean by “a gandhabba”.
– A specific gandhabba (say, corresponding to a human) dies at the end of that “human bhava”. If that lifestream grasps an “animal bhava” next, then an “animal gandhabba” will be born simultaneously with the dying of the “human gandhabba”.
– The possibility of arising of any gandhabba or “grasping of any type of bhava” stops for an Arahant.
2. The “heater coil” analogy given by Lang applies ONLY in specific situations for a human gandhabba.
– A human gandhabba will have a relatively long lifetime (into thousands of years) compared to the lifetimes of “physical human bodies”. A “physical human body” will die anywhere from the baby stage to about 120 years. Thus that human gandhabba will be reborn with different “physical human bodies” MANY TIMES within the lifetime of that gandhabba.
– Exceptions to the above rule apply when a human does an “anantarika/anantariya kamma”. Those are strong kamma that will bring vipaka immediately. However, as long as a gandhabba is INSIDE a “physical human body” that anantariya kamma cannot bring that vipaka. But as soon as that human body dies and the gandhabba comes out of the dead body, that kamma vipaka will perish that gandhabba.
– Now, that can be good or bad depending on the type of the anantariya kamma.
– “Good” ananriya kamma are magga phala and jhana. For example, if that human became a Sakadagami, Anagami, or an Arahant, they cannot be reborn in the human realm. Thus that human gandhabba will perish and a Deva or a Suddhavasa Brahma will be born in the first two cases. In the case of an Arahant, there will be no new gandhabba, Deva, Brahma, or any birth. If that human had cultivated (anariya) jhana, they will be reborn a Brahma.
– “Bad” anantariya kamma includes the killing of a parent or an Arahant. In such a case, the “human gandhabba” will perish when it comes out of the dead physical body and rebirth will occur in an apaya.
– P.S. In the cases of anantariya kamma (good or bad), the coil has been “heated” with that anantariya kamma. But as long the coil (gandhabba) is inside the “body of water (immersed in water)” that body of water will also heat up and be able to keep the coil intact. But as soon as the coil comes out of the water, it cannot “bear” that heat and will burn. This is a CRITICAL point to understand. Please ask again if not clear.
P.P.S. The following video shows such a heater coil. If that heated coil is taken out of the water bucket, it will burn and will no longer be useful.