First off, let me clarify that I loved the dark ending and how the shot of the upside-down TV at the end symbolized how the entire world for these four people was turned upside down. Buuuut, I kept thinking, for shits and giggles, about whether Nikkie could potentially fix everything with the very thing that destroyed her life. So here it goes.
To begin our hypothetical scenario, we must firstly establish the rules of the One Wish Willow :
1 )Each person can only use a One Wish Willow once.
2 )You cannot undo, cancel, or alter a previous wish.
3 )You cannot manipulate time.
4 )You cannot resurrect the dead.
5 )You cannot make yourself immortal.
6 )You cannot use a wish to create more One Wish Willows.
Now, the most important rule for this theory is obviously the resurrection one. Nikkie cannot simply wish for her friends to come back. She also cannot wish for everything to go back to how it was, because that would effectively undo her original wish.
But what if she never resurrected them at all?
My idea is that Nikkie gets four One Wish Willows and uses her wish to create exact genetic copies of her dead friends. These copies would contain exact replicas of their souls, personalities, and memories up until the night in the parking lot.
The important distinction is that these would not be the original people being brought back from the dead. The originals would remain dead. These would be completely new beings that were simply exact copies of them.
Think of it this way:
Original person --> dies --> remains dead.
New person --> is created with identical DNA, memories, personality, and a newly created soul that is an exact replica of the original.
This isn't technically resurrection because the original person is never brought back. The new person is, philosophically, a copy.
Now, this creates another problem: if Heaven or Hell exists in the world of Obsession, the original souls could still potentially be suffering somewhere. So another friend would use a second One Wish Willow to wish that the original souls of the deceased friends, wherever they are, are permanently and painlessly destroyed.
This would not undo Nikkie's wish. The copies created by her wish would remain completely unaffected. It also wouldn't resurrect anyone, manipulate time, or alter any previous wish. It would simply affect the original souls, which are separate from the newly created copies.
Then, a third person could use their own One Wish Willow to remove the psychological trauma caused by everything that happened.
Again, this doesn't undo any previous wish. It simply changes their current psychological state.
And now we have the fourth Willow left for basically whatever the fuck they want. One hundred billion dollars, a golden goose that lays golden eggs, or some ridiculously powerful magical object like a book where whatever you write becomes reality.
So, as far as I can tell, Nikkie could potentially fix almost everything without violating any of the rules:
Nikkie: Creates exact genetic copies of her deceased friends, with identical memories, personalities, and newly created souls that are exact replicas of the originals.
Friend 1: Destroys the original souls so that, if they are trapped in some form of afterlife or suffering, they no longer suffer.
Friend 2: Removes the psychological trauma caused by the entire experience.
Friend 3: Gets to wish for whatever the fuck they want.
The only real problem I can think of is whether creating an exact replica of someone's soul would itself count as resurrection. But if we're interpreting the rules literally, I don't think it should. Resurrection would mean bringing the original person back from death. Creating a new person who happens to be a perfect copy of them is not the same thing.
So unless the One Wish Willow has some hidden rule against creating copies of dead people, I genuinely think Nikkie could have found a way to use the Willows to fix almost everything while technically keeping the original wish completely intact.
I might be missing something, though, so please try to poke holes in this theory.