How frequently is a delayed passing of someone who has reached a severe decline in function for which their passing would be a true blessing, an actual result of deep inner fear keeping them from letting go and transitioning back to the light? What other factors might be involved?

This is the most frequent cause of a person reaching a stage where they are languishing in a kind of torment where the body has, in effect, failed them in a major respect, limiting mobility. They may well be confined to their home or even bedridden, often with pain as a companion and certainly mental anguish with or without physical pain being a factor. There is often a state of depression accompanying the decline because the person is seeing their ending coming and that looming demise triggers many old fears, and even fears generated from the deep subconscious looking at the akashic records and reviewing many death experiences they have had in the past, as well as sojourns in the lower astral plane as an earthbound spirit being tortured by demonic fallen spirits, all of which contributes to the desire to retain a firm grip on life as long as possible. There are many sources of this fear. It is not only fear of death; it can be a fear of judgment as well. There are fears about abandoning one’s loved ones and family because of a strong sense of duty as well as an inborn duty to the self, and many have a very strong drive for self-preservation. This is a basic instinct within everyone and some have this exhibited to a much higher level of intensity. All of these factors work against the person when they are reaching an exit point designed for their escape, they may see as the opposite, as a threat to their very existence, and an end entirely to life itself. Lack of belief in the divine is a major source of distress when people see their time is at hand for the body to give up, and they will fight against this fiercely. You see this instinct described, time and again, in those for whom death comes young as with terminal cancer, that many people describe their loved one who finally succumbed as having been a "real fighter" with a sense of admiration. This reflects how deeply ingrained the fear of death has become in the collective consciousness and unconscious. It is profound, and a testament to the millennia of human existence cut off from major aspects of reality, including the divine origin they enjoy and the immortality of the soul as a given. The current level of unawareness and disbelief denies people these simple comforts.