The events of the episode are all in Nida's head, but the apocalypse does actually happen.
Nida convinces herself that to stop it she needs to murder three people, but it's not actually true. This means that the apocalypse was inevitable and she could have done nothing to stop it. The ending where she walks away with Gaap is actually a hallucination, and she's actually dying from the impact of the nuke.
The flashforward vision Nida gets of the world after Michael Smart gains power shows his party using the "White Bear" symbol, the same symbol used in the talisman Nida owns. What if Gaap's reluctance to let Nida kill him doesn't come from Hell "liking him", but because he's one of their agents? (Gaap does mention he isn't "one of us", but that doesn't mean there isn't any kind of deal in place). The scene where Smart convinces Vicky to vote for him could be read as an use of a Compelling Voice. And consider the scene when Smart survives a car crash, a direct hammer hit, and then the police office appears just at the right time to stop Nida from doing the killing hit. Luck, or an otherwordly power making sure an useful asset stays safe?
The "Justice Parks" seen on White Bear were implemented as part of Micheal Smart's political programee
As some people pointed out in the past, it's strange how the UK would manage to have a public spectacle such as the one seen in White Bear where a not-so-innocent woman ia put through a cycle of torture because of a crime she doesn't even remember because of the memory wipes without breaching multiple conventions and international anti-torture laws... unless, of course, if the UK wasn't the democratic constitutional monarchy we know from our timeline but a fascist shithole run by a dogmatic, totalitarian dictator.
Assuming the events within the plot were really all happening in Nida's Head, or at least the supernatural elements of it, we can assume that there was little to stop Smart from winning the election and implementing his tyranical policies - and given that the White Bear symbol used by his "Britannia Party" is the same as the one used through the aforementioned White Bear episode, it isn't difficult to connect the dots here - that the "Justice Parks" were created in order to punish enemies of his regime or perhaps even use them as examples - it is a public "attraction" after all and it's the type of sadistic entertainment a secretly sociopathic person like him would support.
There are multiple realities coinciding with this one that the demon's in Gap's home realm have access to.
Nida's quest has absurdly high stakes and is blatantly difficult to achieve, and the caveats of it, such as her third murder not counting because the person was a murderer, do nothing but further impede her. It almost seemed as if her and Gaap were doomed to fail from the start, which is odd considering how Hell seems to be at least somewhat invested in the human realm considering how eager they were to watch Michael Smart progress in his villainy. You'd think that the pair would be thrown a bone if the consequences of failure meant Smart not achieving any of the goals they were looking forward to. After all, if Nida succeeded in killing Smart, even if it cost the demons a horrible human, at least the world wouldn't end and eventually someone just as depraved would be born, but the world ending means this can never happen.... unless you believe that the demons have access to alternate realities and can access different versions of Earth where an apocalypse isn't predicated by the actions of a single woman. They wouldn't be too broken up about the world ending if there's more than one world to manipulate, after all.
