How can the ending be any sadder? Would you really prefer it if Eren were to just continue with the rumbling and kill off every. single. character.
Isayama killed off characters who were no longer important to the plot but who we still had emotional attachment to (Jean, Connie, Gabi). *We see Annie see her father turn into a titan right before her eyes, this was literally one of the most brutal final chapters we could've gotten.
The final quote of the chapter is literally "To the boy who sought freedom... Goodbye." If Eren were to be revived after this it would literally just be a huge cop-out.