idk, wait until the next part of the novel comes out. But I'll tell you now, they very rarely straight kill Planeswalkers (only one I can think of is Venser is the only confirmed PW death, but I haven't read much before Ravnica: City of Guilds so I could be wrong). But anyway, they have worked to hard to flesh out Elspeth as a character in this block, they wouldn't just end it. Ask me in a few weeks and I'll have a better answer, I want to read the rest of the novel. (Baseless speculation, we know Elspeth kills Xenagos, God of Revels as seen in Deicide for almost destroying Nyx, maybe Erebos was talking about finally getting Xenagos).
MAJOR THEROS NOVEL SPOILERS!!! Keep reading at your risk
About my last post, the first little bit of the book is about Daxos meeting Elspeth, and Elspeth obtaining what would eventually become the Godsend (it was Purphoros's Sword). Before they met, Daxos's mother was taking him to the Temple of Silence (Atheros's Temple) to see if there was a remedy for Daxos's "condition" which was just he could see Nyx and speak and understand the language of the Gods and the Nyxborn. Before Daxos and his mother got out of the Temple Atheros was using his Scythe to try and get Daxos for Erebos, but after he got caught his mother somehow freed him in exchange for her life, so maybe it's just Erebos was refering to finally killing Daxos. idk