Solitär
I'm probably not the only one thinking this, but I think she's still alive. She was such a great antagonist and foil to Frieren (this post explains why very well) that I find it very odd she would just end up being a secondary antagonist in Macht's arc. Not to mention she admitted to being very careful, cowardly, and wary of humanity. Furthermore, she had analyzed Frieren's mana after her fight with Aura and concluded she was suppressing it. There's no way she would have faced her head on without taking precautions. There's a reason she was nameless great demon.
There's a very easy way she could have survived: the duplication magic Land uses. He could create perfect clones of himself only Serie could see through, it's an ideal way to fake one's death. We know Solitär has been studying human magic extensively, it wouldn't be far-fetched for her to have mastered this spell.
Her showing up in the time travel arc just reinforced my belief we aren't done wit her. What do you think?