SO basically people are saying: “Life” means the parts are generally working. Life is a whole series of reactions that keep the bag of chemicals in a relatively steady state.
When everything is working, food gets turned into nourishment, oxygen is absorbed and CO2 exhaled by breathing, the heart uses some of that to pump the rest around the body for use by the rest of the body. SOme of that is used by the chest muscles to keep breathing going, some by the brain to produce the neurlogical electrical impulses that keep other parts going.
When any of these systems fail, the cascade effect can cause the whole system to eventually grind to a halt. No oxygen, no food, not enough water - all can cause parts of the body to stop functioning, which in turn cause more to fail. If not restored in time, the chemical effects of this failure become irreversible. If reversed but too late, some parts may not function properly.
What is the seat of someone’s personality? Experience and the history of brain-damage victims has given us a rough map of what parts of the brain are responsible for what functions. Damage this part, you cut off higher reasoning; this part, you cannot see; this part and lose control over this function, etc.
As a result, most medical ethicists agree that a person is actually dead when they no longer have the electrical function of their neurons. Whether that is reversible or not, and for how long, depends on a lot of factors. Drowning in cold water can mean you may revive up to an hour later; the younger, the more resilient, etc. If you com back with brain damage, are you still the same person?
What makes someone a person? If you can really answer that there is a seat at a prestigious university waiting for you.
SIDS was, IIRC, generally attributed to a form of suffocation (among many unrealsted reasons); about 15 years ago they found that the incidence was drastically reduced by not leting children sleep on their stomach. Nothing magical about it - for some reason, some system stops. Like any other death cause, it then cascades into total system failure. If not found and reversed in time, it is permanent.
So there - if a person might be revived, even temporarily, why would the “soul” “depart” and a certain moment? Just to journey that long corridor with alight at the end? Who knows. As pointed out, there’s not been a serious collection of definite studies of any weight loss.
Besides, from a pure physics standpoint - what extra weight? You are the same bag of chemicals before and after. Every atom has a particular weight. Added up, it’s your body mass weight. If you are going to rewrite the fundamental laws of physics, better be prepared to explain how.
Physics basically says “if you can’t devise an experiment to test it, it’s not science”.