What happened to certain characters? Will we ever know?
1. Master Yu and Xin Fu were trapped in that metal box that Toph got out of. Do you think they ever learned to metalbend their own way out, or (like Xin Fu said, "I'm going to be stuck in here with you forever, aren't I?") died in there due to starvation and dehydration?
2. Fire Sage Shyu, along with the other 4 Sages in Roku's Temple, were captured by Commander Zhao and made guilty, even though only Shyu was. There are other "Capital" Fire Sages in the Fire Nation Palace, but we never saw the Temple Sages again. What do you think happened to the 5 originally seen Sages? If found in a Palace prison, they could have been released by Zuko, but we never knew what prison they went to...
3. And when Azula banished Lo from the Palace but pointed to Li, the identical twins were left confused as to who could stay and who was banished. They were last seen after this order. What happened to them? Although very elderly and died way before Team Avatar, did the twins split up and one leave the Fire Nation? If so, which one? And whether one of them being banished or not, what did Lo and Li do after the war, mainly being Azula's firebending mentors?