He was killed when Rand al'Thor reached the Eye and was confronted by Balthamel and Aginor. Someshta killed Balthamel at the cost of his own life. In his final moments, a tree sprung up at the exact location he fell. His garden began falling to the Blight, but the Ogier Loial used his treesinging abilities to keep his tree alive.
When Rand al'Thor passed through the glass columns ter'angreal in the Heart of Rhuidean, he glimpsed the life of Jonai, a Da'shain Aiel during the Breaking of the World. At a meeting in the Hall of Servants, Jonai was drawn away from the conversation the Aes Sedai were having, and went over to Someshta sitting in a corner. Though Jonai professed to be his friend, Someshta did not remember him. Later during this meeting, the Aes Sedai asked of Someshta a "task for the last of the Nym." While is it unspecified in the book what this task was, it can be inferred that it was to guard the Eye of the World until the Dragon was reborn.
Someshta was mentioned again as Rand traveled further through the ter'angreal. He viewed the life of Coumin, another Da'shain Aiel during the War of Power before the Breaking. Someshta was assisting in a seed singing that Coumin too was participating in. It was noted that he had spoken to Someshta on previous occasions and wanted to ask him if the stories his greatfather Charn told him of the time before the War of Power were true. This points out that he was at least three thousand years old when he died and probably much much older. It was believed by some of the Da'shain Aiel that the Nym never died.