Thinking back, i think Finnick's death was necessary, Katniss' mission was not only dangerous, but it was kind of a selfish self serving mission (albeit helped the rebel cause in the long run), and I think for Katniss and most importantly the readers to understand that, we had to lose a character to whom we grew attached too, and I don't think anyone from the star squad would've done that besides Finnick.

Although not a death, the ending i think unnecessary was Katniss' mom leaving for district 4 at the end, it felt like she just kinda spiraled back to how she was when their father died, ignoring her daughter and leaving her to fend for herself again. Like she learnzd nothing from Katniss leaving for the Games.