Death is the cessation of all biological functions that sustain any living organism. Situations which commonly bring about death include aging, malnutrition, disease, suicide, murder and acidents or trauma resulting in terminal injuries. The physical bodies of all living organisms begin to decompose shortly after death. There is no scientific evidence yet that suggests consciousness survives after death, nor even that dead people are reborn or move to another plane or dimension to live a new form of life.
The word death comes from the Old English deað, which in turn comes from Proto-Germanic *dauþaz (reconstructed by etymological analysis). This comes from the Proto-Indo-European stem *dheu- meaning the "Process, act, condition of dying".
In society, the nature of death and humanity's awareness of its own mortality has for millennia been a concern of the world's religious traditions and of philosophical inquiry. This includes belief in resurrection (associated with the three Abrahamic faiths), reincarnation or rebirth (associated with Dharmic reliions), or that consciousness permanently ceases to exist, known as eternal oblivion (often associated with atheism).
Commemoration ceremonies after the death of a human being may include various mourning periods and other funeral practices. The physical remains of a person, commonly known as a corpse or body, are usually interred whole or cremated, based on prevailing cultures. The Zoroastrians feed their dead to trained vultures who are kept confined in cages in their cemeteries.
Most people suffer great pain and loss when a family member or close friend passes away. The natural bond of human attraction finds it always very difficult to let go when a person moves on. The loss, basically, is the one suffered by the living for the dead have not lost anything at all to be sad for, even if they could.
This simple fact of life only proves that we are not a lonely species and that we need our loved ones alongside us for as long as possible to be loved and lived through our lives. The bonding between people also emanates from the close proximity, common values, and upbringing they cultivate since birth.
It is plainly seen that the most certain event in life is death. Everything else could easily be a variable to many degrees. While the time and form of death is certainly unpredictable the fact that that it will happen at some point of time in the future is non negotiable.
Most often the sadness is accompanied by the reminiscing of the wonderful times that were shared with the departed. In some cases regret accompanies this sadness in that the living automatically feel that they could have done better to the deceased during their lifetime. But then it is too late now and this usually causes some despair and anxiety in the minds of many.
At the end of the day the only salvation we can get from the death of a creature is if we have been compassionate towards them during their lifetime.
May All beings be Happy.