From an evolutionary point of view, you could say that death is adaptive. Not to the individual of course, but to the population as a whole; we are born, raised under the protection of adults until we are capable of looking after ourselves, if we are lucky we survive to reproduce, then long enough to look after our children and perhaps the next generation too. If the organism can no longer reproduce, it no longer serves a purpose. Why do we live as long as we do and no longer? Evolution has shaped it. Why do we die? To enable the next generation to live. However, what if human evolution could overcome these limitations? If the issue of limited resources could be dealt with, medical science may be able to sustain or replace our failing organs indefinitely, and we could then choose when we die. I would not choose immortality if it were offered; I believe there can be no appreciation of life without the possibility of death. But would I choose to extend my life beyond my anticipated 70 or 80 years? Most definitely. Finite, but longer, that would be perfect...!