i doubt he'll die, i mean, yeah he will die, but not because of the final fight, i think it will go around something like this:
*epic fight with firelord while zuko fights azula*
Fire Lord: You put up a good fight, but you're still a kid, prepare to die, a virgin! *shoots lightning*
Aang: *flinches because of the memory of azula and the lightning, so he gets hit* *thinking* i failed... in the end, i am just a kid... i am not a god, or a hero... it would have been best if i had never awoken from that iceberg... heh, to think i actually believed i, a 13 year old could defeat so many people who have trained their entire lives to become powerful, i didn't even train a year... now, everyone that ever helped me will die... zuko, sokka, toph, foaming mouth guy, and, of course... you... katara, you gave me so much strengh, but also weakness, if hadn't refused to leave you back then... i would have obtain the power of the avatar state... i made a mistake... no, that cannot be right, that can't be right! i know my duty is to save the world, but caring so much for you can't be wrong, you have been a friend, a mother, and everything to me, if it hadn't been for katara i wouldn't have gone out of the iceberg, i wouldn't have helped all those people, i wouldn't have brought hope to everyone, including my self, i can't give up, no, not yet, not while i can do something! *wakes up and sees FL preparing a final hit* *firebends a little to escape his attack*
FL: ?! you should be dead
Aang: Not... While... I... Can... Protect... Her... Even, if that... Means i must... Leave her... *has vision of him with the whole avatar state thing from CoD* And... now... i... Can! (goes avatar state and kicks the holy snot out of the firelord)
Meh, i do bad fanfics =P
Anyway, yeah, he will kinda die, the pull out the Avatar State and save the day, then he will die about 100 years later and stuff, it's likely we hear something about his leyend, "Being the first and only avatar that knew his idententy at the age of 12, he stopped a 100-year old war, and repopulated the Air Nomads, Avatar Aang."