Luckily she isn't confirmed to be dead– she just took the Sylex and yeeted it into the blind eternities. The Invasion Tree had already connected to non-Phyrexian worlds and if the Sylex was allowed to detonate, it ran the risk of destroying all of them in addition to New Phyrexia. It is implied that Jace telepathically sent Elspeth a new plan right before he was fully Compleated and the Sylex exploded, so Elspeth had to carry through the plan.
My guess is Elspeth is going to return even stronger in the next set. Call her William Afton because she always comes back.
Honestly, this just showcases one of the things I don't like about the current Phyrexia storyline — they've buffed Phyrexia way too much, to the point where it actually loses some of its impact for me.
They went from "scary inevitable threat that's contained on a single plane, but the seeds for something similar might have been scattered across the multiverse because Urza has Good Ideas" to "THEY HAVE PLANESWALKERS AND PORTALS THAT THEY CAN SEND ARMIES THROUGH DIRECTLY CONNECTED TO TWELVE WORLDS" in the space of, like,
two sets. The thing that makes successfully Compleated planeswalkers scary (the fact that they're non-planebound infection vectors for the Cyborg Zombie Body-Horror Plague) gets overshadowed by the fact that New Phyrexia can
already launch invasion forces against other planes.
WotC's spending their build-up
really quickly, is what I'm saying.
On top of that... this entire set is kinda predicated on characters making
incredibly poor decisions. It honestly feels like they pulled the planeswalkers they were going to send out of a hat — you have the two Kamigawans (which, sure, why not, they were around when Tamiyo was taken), Miss Warcrimes (Nahiri), Four People Whose Powers Involve Directly Interacting With Infection Vectors (Jace, Lukka, Nissa, and Tyvar), Miss She-Came-Along-Because-It-Makes-Jace's-Compleation-Sadder (Vraska), and Two Ladies Immune To Phyresis (Elspeth's confirmed to be immune, while Kaya is probably immune because she's only intermittently corporeal).
Like, why send
half of those people when you could've sent Chandra? No, seriously, why is she hanging back on guard duty? If you're planning to destroy the place
anyway, why not send the lady who is arguably the most destructive living planeswalker? Sure, she's an idiot (not that that stopped them from bringing Lukka...), but Phyrexia just murdered her mentor
and she's so Red-aligned that Compleation would just mean that she'd start hanging out with Urabrask (you can't tell me that she'd end up anywhere but with the "consent is beautiful" Phyrexians).
...
Actually, that brings up a really good question: why trust Jace
at all once he's been infected? The oil starts messing with your head almost immediately, so anyone who's showing
any symptoms should be treated as if they were
deeply unreliable at best, and actively a sleeper agent at worst. Heck, that's
another reason why they shouldn't have brought Jace along — his whole thing is that he's
really good at screwing with people's heads.
Are we sure that Jace wasn't a sleeper agent before this set? That'd make a
lot of things make more sense...