I will make this short.... An ever repeating theme in Avatar has been death. And what this has shown us again and again is that death is not percieved negatively or as a punishment, just as another journey.
So killing Ozai would not be the ultimate punishment (there has to be somthign else...) Also in relation Aang has reflected over and over again the value and sanctity of someones life, no matter who they are; wether it be giving people second chances (Zuko) or that anyone is capable of great love or great evil (Avatar and the Firelord). (if ya dont know what im on about listen to dongufeng.com "From the Spirit World Podcast")
So i think the possibility of Aang sparing Oza's life would be as Axrendale said , a smart ending. It would be the ultimate conclusion to Aang's chracter development if depsite everything he kept to his morals and values and preserved life, rather than racked up the courage to end it.
And one last point, it said in the summary on the nick.com website for Episode 320: Book 3 Volume 4 DVD that "will Aang have the heart to defeat the Fielord?" I think the fact that this was included in a one sentance summary for the episode means a main plot point that maybe Aang will have issues with killng Ozai. Just my two cents worth
Edited on 07/11/2008 11:50pm