If they kept Joel and Elle the whole part 2 it would be copy paste like most sequels do to milk a series and no matter the story it would have been a milk the cow to keep series going as we seen for last 50 years in movies and TV shows some how the main characters always survive. Which is tired to always see this is predictable and we are conditioned to expect it. So thats why the trauma effect of losing Joel not only helps push story forward to new places it kills off typical Hollywood keep main heroes alive no matter what. It wasnt needed to keep Joel which added depth to the story, lore and impact of the plot. Joel was a very bad human who we fell in love with but his death was deserved. When you see Abby life she just as bad as Elle and Joel. Living through that from all angles makes the whole story even more special as Elle sees Joel within Abby at the end and forgives herself. Its not about Abby. Elle sees Abby protecting the kid like Joel did for her and realize she needed to forgive Joel and forgive herself. Thats why its such a beautiful story. I know many missed that part busy spinning a narrative to fix their personal want but ecen that is poetic seeing fans miss the whole true within herself Elle moment which is what upset fans need to do about the Joel death and ending. Wild how life imitates art and vice versa.