No, I don’t mind any spoilers.
I now understand. This sounds more like a Sci-fi series.
So, those who were murdered or died from illness or injury actually suffered death.
What happens to the main characters? Does Michael and Walt return to the island?
Most of the characters did die eventually. Jack, Hurley, Kate, Sayid, Aaron, and Sun made it off the island but then returned at the behest of Jacob. Locke also eventually made it off but then died in LA, a major plot point later in the series. There were very few of the original cast who survived to the end, but Sawyer, Kate, and Claire eventually made it off at the end with a few other characters introduced in later seasons. Hurley survived and became the new ‘Jacob’, with Ben as his right hand. Together, the two of them eventually go back to fetch Walt and bring him back to the island, where he supposedly belonged (Walt was at the same mental hospital as Hurley was).
Michael died in season 4, he returned at the behest of Ben to help out his fellow castaways as an act of penance, and he died saving Jin. Jack died at the very end of the show, having saved the island from destruction, leaving Hurley Ben and Desmond, as well as Rose and Bernard, who also never left as they wanted to make their life there. Desmond would eventually go home since Hurley was in charge which gave him the powers to come and go as he pleased and also allow others to reach the island and leave if he so deemed it. Sun, Jin, and Sayid died in a submarine mishap caused by the Man in Black, who was eventually killed by Jack and Kate.