There are several deaths throughout The Adventures of Huckleberry Finn. The first one would be the symbolic death of Huck. Huck fakes his death to get away from Pap and is metaphorically reborn on the river. It's important to note that on the river Huck is Huck. Every time Huck goes ashore, he changes identity and becomes someone else.  Huck is only his "true self" on the raft. This is a death and rebirth cycle Huck experiences throughout the novel.

Other important deaths include:

• Pap--Pap gets killed in a poker game, probably for cheating.  His body is found when Huck and Jim board the house floating down the river.  Jim covers up the body and keeps Pap's death a secret from Huck until later in the novel.
• Miss Watson--It's never stated how Miss Watson dies, but it was probably from old age.  Huck finds out about Miss Watson's death from Tom Sawyer at the Phelps farm.  He also finds out that Jim was set free after Miss Watson passed.
• Buck Grangerford--Buck is a young boy, the same age as Huck, who is killed by the Shepardsons during a feud of unknown origin.  A variety of Grangerfords and Shepardsons are killed as well during the battle between the two families.  
• A drunk, named Boggs, gets killed by Colonel Sherburn in an episode where Huck goes to a circus.  There is some sort of bad blood between the Boggs and Sherburn, and Boggs insults Sherburn.  Sherburn gives Boggs an ultimatum to get out of town, and when Boggs doesn't leave, Sherburn shoots him in cold blood.
• The robbers on the boat, the "Walter Scott," drown before Huck can get help to save them.  It's implied that they were probably the men in the poker game who killed Pap.