We're at a point where the only option where Sylvanas dies in the story will be the one that she chooses to. Because that's what the whole story has been moving towards - Sylvanas was never given the choice. Anduin literally says it to her - "You never had the choice...!". Watch that cinematic again (Anduin before he gets turned), and you can see exactly what motivates Sylvanas to doing all this bullcrap. Killing all those people, making people 'join our cause, or be made to serve', 'Horde means NOTHING!', breaking the Helm of Domination... All of that is a result of Sylvanas not having a choice to die on her own terms and being forcefully brought back into life to serve others. She thought she would gain choice by joining Zovaal, for a greater purpose of breaking the cycle; but instead we see Zovaal betray her and treat her as a servant - a moment where Sylvanas realizes she
still has no choice. So the obvious fitting end is if she goes out *on her own terms*, the only real choice she has left in her life.