great, insightful questions, guys!
Bruce asks questions about a situation I've often written about but about which I don't know of any authoritative spirit guidance. My own references to near-death-experience have usually been when making the point that those who have had an NDE did not actually die and then return to life. In such discussions I've also made the point that death occurs when body and soul separate permanently. But I haven't ever considered the mechanism, the actual point when this so-called silver cord is said to break.
I can't remember anyone asking about the chronology of the event either, the "What comes first, the chicken or the egg?" situation. Here we're considering whether death comes first followed by the cord breaking or whether the cord breaking results in death. I'll offer my thoughts but first the preamble.
I see an individual as a composite of "body and soul". The individual's spirit/soul animates her/his body and maintains (what we consider to be) life. When we die separation of body and spirit/soul occurs, the body decays, the spirit carries on to do something else. In my model of life incarnate it is down to a deliberate separation, a 'pulling-away' from the body by the spirit, that brings about the death of that body which we view as the death of the person. The reasons for this will vary.
As I see the situation, it's the decision to make the separation that then leads the spirit/soul to part company with the body by severing the 'tether', the 'umbilical', the 'silver cord'. The actual severing of that cord defines the point of our death, the "no going back" point. (Exactly how a soul/spirit brings about the separation is as unclear to me as the way it brings about the fusion of itself to the egg/embryo inside the mother to be.)
Several reasons for severing the cord appear immediately obvious. The first might be because the soul/spirit concludes there is nothing useful to be gained by continuing to struggle on in a worn out body.
The next might be because the spirit/soul simply cannot maintain the processes needed to keep its body alive, even if it would prefer to continue. That might also apply in the case of someone deliberately ending their life for whatever reason.
Or it might be that the soul/spirit recognises that it has fulfilled enough of its intentions and/or the plans it made before entering life as an incarnate. Or maybe that it had met the commitments it made towards others as part of their so-called life plans.
And there might be any number of other reasons.