what purpose(s) does hucks death serve?

I'm assuming that you are referring to Huck faking his own death. This takes place in chapter 6-7. Huck really needed to get away from his drunken abusive father. Faking his own death was a good way to prevent his pap from pursuing him. He also needed a long break from the Widow Douglas who was constantly trying to turn him into a civilized gentleman.