Well, technically only Aang and Sokka have been confirmed as dead. Oh, and it can be assumed, Zuko's parents. Otherwise, Katara is still obviously alive, and we still have potential to see an old Toph, Suki, Zuko, Mai, Ty Lee, Azula, etc. As a matter of fact, we've even seen people live to be past 100 (i.e. Guru Pathik), so who knows, we might see a way-over-the-hill Iroh.
“…Judge not what a man has done, but judge what he could have done if he was a different bloke altogether. For art thou a leper? And a leper can changeth his spots…” --Rudy Wade, Misfits (Series 4, Episode 8)