Ok, using the art of deduction, I have narrowed the candidates down to a short list of possibilities.

Beware that I am very good at deduction. I am absolutely certain that one or more of these people will die. Don't read the list if you don't want to be spoiled.

Aang

Katara

Sokka

Toph

Zuko

Ozai

Iroh

Azula

Suki

Hakoda

Ty Lee

Mai

Teo

The Duke

Haru

Chit Sang

Appa

Momo

Chief Arnook

Pakku

Bato

The Boulder

The Hippo

The Mechanist

Due

Tho

Hue

Bumi

Admiral **** (Which is censored, for some reason)

His son, who is also called **** (And also censored for some reason)

Ruon-Jian

Jeong Jeong

Cabbage Guy

Foamy

Hama

Piandao

Onji

Dock/Xu/Bushi

Ming

Ursa

Lo

Li

Gran gran Kanna

Sokka and Katara's unnamed mother

Aunt Wu

General How

Someone else with General as their title

Someone with a vowel in their name

Someone with no vowels in their name

No one

...

There you go. I predict that at least one of those things listed will die. You know I'm right.

"BOB THE FREAKIN' BUILDER!!!"

*laughing my head off* Oh, my god! *continueing to laugh* Oh, I promised I wouldn't wet myself. *laughs some more, starts to choke and dies*
Koji: *chants resound until I wake up*
..............*continues to laugh*
Koji: I did that so you wouldn't laugh, you moron!

MAI CANT/WONT DIE! BECAUSE *covers mouth*

I have a feeling Ozai will/might die.

I doubt anyone will die, except the Fire Lord, of course. Maybe Azula.

Iroh, Toph, Ozai, and (someone SplitReflection forgot) Long Feng.

Iroh will be killed in the only way it is allowed, after an uber battle with PL Ozai after the comet comes.

Toph will die to protect Sokka from... something. It is there she will confess her love to him.

Ozai, killed by Aang.

Long Feng, killed by Azula after... *takes a deep breath*

...he reveals that he affected Zuko decision in CoD to side with Azula. He knew of her plan to betray him all along and realized that he had to play along in order to get true power. If he won Ba Sing Se, either Aang would remove him and restore the Earth King or the FN would take it when Sozin's Comet returned. So, what he decided to do was ensure that Azula took Ba Sing Se. To do that, he needed to make sure Zuko was on her side during the fight, so he hypnotized him. Since he didn't have that much time, Zuko wasn't able to be completely brainwashed to be on Azula's side, hence the character development occurred.

Well, after Aang kills Ozai, Long Feng turns up and crushes Ozai's corpse with stones. He then reveals that he will take all of the glory for killing Ozai and claim that Ozai killed Aang. He has no fear of retribution, because he doubts that Aang would guide the next avatar to avenge the "Greatest Hero of the War" (i.e. what Long Feng will be called). However, to make this work, he needs Aang's body, and the bodies of the others, to be burnt to death, not crushed, so that it looks convincing. Aang at the moment is in desperate need of healing, since he just fought Ozai, the others are exhausted as well, due to their battles, however, thanks to the comet, Zuko has enough power left to fight back. At that moment, Long Feng says that magical, wonderful phrase that shows the voodoo that he do so well.

"Zuko, the Earth King has invited you to Lake Laogai."

With that as the cue to start the show, Zuko engages in one last epic battle with the Gaang. This time, with Long Feng's aid. He plans to have make Zuko use fire on himself as soon as he's killed the others. Well, the epic battle ensues and they are all trying to survive, fight back, and get Zuko back to his senses. Suddenly, someone, maybe Ursa but it doesn't have to be, tells Zuko, "Never forget who you are." That triggers Zuko's memories and weakens Long Feng's mind control. Long Feng notices this and once again says that the Earth King has invited him to Lake Laogai. This battle goes back and forth for a few moments until Long Feng knocks out which ever Gaang member was saying it.

Then, just as Long Feng is about to say his line again for the last time and get Zuko to kill everyone in the Gaang...

BAM!

A lightening bolt hits him the same way that one hit Aang in CoD.

The camera pans over a distance behind him and we see Azula in her lightening bolt pose. Long Feng falls dead and Azula delivers an awesome one liner about how no one beats her at her game. She then acknowledges the surrender of the FN and disappears, never to be seen again unless she wishes to be.