What happens when all the ghosts’ desires are fulfilled? Do they go away or stop possessing the concerned person?
It is next to impossible for a ghost’s desires to be fulfilled. They get even more entrenched in their desires with each fulfilment. Ghosts generally do not go away, unless the person himself has become more saattvik. Then the ghost is forced to leave due to the spiritual purity of the person.
In the case of departed ancestors, they continue to trouble us throughout our lives unless we do something to help them to fulfil their desires or move on in their afterlife, as the case may be. In fact there are cases where the ancestors have troubled their descendants throughout their lives and even continued to do so when the descendants died and began their afterlife.