In ATLA, no one died. NO ONE.
But....in LOK, Book 1 enemies died and Book 2...I'm still not sure what happened to him :/
LOK storywriters are not that cruel, it was the same two guys who created ATLA. They will not kill off Tenzin. Important, loved characters only die in those stories like Death Note ;(
poor light....r.i.p.
Remember Jet? They killed him off, but it was too vague.
Apparently that was going to be much more blatant than it was, but the people at Nickelodeon had then take a more ambiguous route (which they've lampooned in The Ember Island Players and several times in LoK).