According to the search results, Sokka died sometime between 158 and 170 AG, and the cause of death is believed to be natural, as he would have been between 74-86 years old. The last known sighting of Sokka came in 158 AG, when he was 74 years old. This occasion saw Sokka and others protect Korra, the next Avatar, from a group called Red Lotus. But, by the time The Legend of Korras main story takes place in 170 AG, Sokka had passed away. The exact details surrounding his death are not known, but some people speculate that he may have been killed by the Red Lotus leaders, given their willingness to kill people, especially world leaders, since Sokka was technically one at the time. However, this is just a theory, and there is no concrete information on how he passed away.