MOCKINGJAY: It wasn't necessary for Finnick to DIE!?

I know it's just a book.... EVEN THOUGH IT THE SERIES WAS AMAZING.... I was deeply saddened that Suzanne Collins MADE FINNICK DIE! UGHHHH! And it's as if she didn't even put much thought into the part! He was my favorite character and I just adore the part where he had no pants and Katniss says, "Maybe some pants?" AHHHH my favorite part xD