Is Ymir dead in Season 4?
Ymir obtained the powers of the “Jaw titan” (one of the nine) by eating Marcel, Reiner and Bertholdt’s friend. So yes, all signs point to the “lion looking” titan in Season 4 Episode 1 having Ymir’s powers. Ymir is most likely dead.
Is YMIR dead in Season 3?
Yes she did die. She was eaten so that a new person could become the Jaw Titan. She chose to go with Reiner and Bertholt because she used to be a mindless titan but she ate their friend Marcel, and turned into a human again. She said to think of it as returning something that she borrowed.