This is an idea I've had for a while, being more of a "Re:Forgotten" fic where Subaru dies permanently and having an exclusive focus for Satella.

  A little plot below:

  “It was right after his execution before the entire capital.  After an attack by Capella, where many died, Lugnica finally declared war on the Cult of the Witch.  Descended to eliminate any threats related to them.

  At the same time "his" his head rolled across the floor and the crowd cheered, a strong bolt of lightning struck the castle.  It was as if the world was announcing something.
  Then, beyond the watchtower on the omen dunes, a huge wall made of purple crystals began to crack.  No one could ever notice the silhouette trapped inside the crystal, opening its purposefully charged amethyst eyes."

  In short, Satella breaks free of the seal and seeks to keep Subaru's soul for herself, protecting him once and for all.  However, it is still "incomplete", so Satella sends her "jealous" counterpart to retrieve the remaining wizarding factors.

  At the same time, Satella has to deal with the arrival of a volcano which states that she must not leave the seal until the "prophecy" is fulfilled.  However, Satella retorts that the "prophecy" has already been killed and now there is nothing left.  Vulcania is startled by this revelation, but decides to keep the "pact" made long ago and try to make Satella back down.  A fight ensues, and the outcome remains unknown.

  This fic is basically a "Tatakae" version of Eren/Satella.  Where she basically declares war on the world, with the aim of getting someone to kill her, as her "beloved" is no longer available to do so.  The key to defeating Satella besides Subaru is pretty "obvious" if anyone asked lol...

  Anyway, there are some cool points I thought about this plot:

  1- About Subaru's memories returning to the world.  It would only occur after envy had killed all the archbishops.

  2 - Speaking of the Witch of Envy, I think it would be cool if the two had separate bodies.  With Satella in the physical body and Envy in the astral body (His shadow form).

  3- Satella's Declaration of War, right after everyone regains their memories of Subaru, would be to throw Volcanica's dead head in front of everyone.  A way of saying no more a "God" to protect them.

  4- the other countries are also threatened, forcing them to make some kind of Alliance to prevent the return of the Witch.

  5- Satella's main objective is to completely unite with her "beloved" without leaving anything behind.  That's why she seeks to "bully" the entire world so they'll find a way to kill her.  Of course, no one knows about this desire of hers.

  6- The Witch cult was massacred by envy.  Pandora apparently gave up on her plan when one of the "keys" was lost.

  Then that's it!  A story of a jealous witch, causing destruction wherever she goes, only to have her head ripped off at the end.  The coolest point I thought of in this part where Satella, before she dies, releases the memories of Subaru's loops to the world.  Similar to what Eren does in Attack on Titans.