As we currently stand, death is indeed certain and inevitable (unlike Thanos...), but in the future that is an uncertainty as a few years ago scientists found a fish that never gets old, his cells never grow old and thus making him immortal or rather "cheat" time. As he is never immortal since he can still be killed. If humans can achieve such ways, I bet a whole new branch of discussion would open up as to people deciding if they wanted to leave or keep living, for instance.
But as we stand now, death will take us one by one eventually.
But us, humans, often misjudge the worth of some ppl and things and only realize how much they mean to us when they are gone. I doubt a person that never cared for another will cry for him/her unless they are twisted or someone they trully care is struggling hard with this person death or they didn't realize they cared that much about the dead person. Either of the options are valid, and I've been tho the second before. Someone that meant the world to me lost someone I didn't particularly liked nor disliked, In fact I might have even disliked the person and when the said person died and I've seen the person whom I cared struggle so bad, I couldn't help to feel sad and cry along.
Whatever makes us cry cuz of someone's death will always be the same, our human nature, being it humanly or tainted!