First, I have always understood nephesh to mean 'soul', yet you define it here as 'life'. How would you distinguish therefore between the concept of nephesh and the concept of chay?Starting with the second question: What I was trying to do here is laying out some ground work for developing a fully fledged biblical concept of physical life. It may not seem that challenging if such a position happens to coincide with secular definitions—for which we should be grateful—but it is important for us to have the right reasons. A libertarian and drunkard may both decry Prohibition, but they do so from different positions. It may be that the secular arguments around death derive, in part, from our Western Christian heritage, though definitions of life are being challenged by medical ethicists in the literature and abortionettes in the culture war.
Second, you mention that this might have implications on how we view euthanasia, abortion, ect... I don't really see how since we already define death in those terms. Within general culture the cessation of the heart is still the prinicple symbol of the moment of death. Thus, I am not sure how challenging this is. Could you elaborate on how you feel this would alter people's perceptions?
I have considered this matter for some time, not all my thoughts included in the post; it seems to me that blood is closely tied to life which is what I was establishing in the post. But because this connection is foundational it is important to maximise certainty before deriving corollaries.
There are arguments around abortion and euthanasia relating to personhood, though personhood may not completely equate to living—animals have the latter, not the former. If the commandments of God (eg. Do not kill) are based on human life—even if the reason for the commandments is the imago Dei—then we need to consider how being alive affects permissible behaviour.
Regarding the first question I am afraid I cannot answer this to any degree of satisfaction. I included the Hebrew words to show which word occurs where, and to emphasise the repetition of the word "blood". I do not read Hebrew so my thoughts are somewhat restricted. I understand about unwarranted expansion of semantic ranges, but I am also cautious about undue restriction based on word use: biblical narrative, and even more so poetry, uses frequent parallelism which relies on the use of synonyms; we should caution against making non-existent distinctions between synonyms.
That said, I understand nephesh to roughly parallel the English "life", or perhaps "soul"? It applies to humans and higher animals, and is related to the concept of breathing. Plants and some creatures classified Animalia are not living in the nephesh sense. So perhaps "soul" is a better translation? We will then need to grant that a cow may have a soul, but in a Hebrew biblical sense, and not necessarily in an English sense? I am uncertain how this relates to chay, though chay as life seems to also contain the meaning (or be metaphorical for) "newness" or "freshness".