Friends with Tax Benefits + Drift AU
Friends with Tax Benefits + Drift AU is a sub-AU that combines Friends with Tax Benefits AU and Drift AU. Yup, we're crazy. We are mixing AUs of AUs to create AUs of AUs of AUs.
Two possibilities here thanks to the Drift AU split!
Bad End Drift AU
Dipper loses Mabel only a few years after taking her soul to save her. He very likely spirals further into his demonic side, driven by the pain of having lost his sister after so much effort spent to reconnect with her. He’s already pretty much chaotic evil, and Henry doesn’t trust him at all, not even around the kids. Without Mabel there to hold them together, they most likely wouldn’t stick with each other by mutual choice.
For that matter, it’s possible that Willow doesn’t survive the birth either. Without the trust of Henry or Stan, there might not be the deal to save her. Or maybe there is, but it’ll cost a lot more than a year of life between them, and when Mabel dies what little trust they placed in him for that deal is killed as well.
Either way, there wouldn’t be any kind of marriage for tax benefits. Henry might even try to keep Dipper away from himself and the kids entirely - wards, exorcisms, barriers, demon traps, whatever he can possibly think of. Dipper still gets through and mocks the attempts. He may have lost Mabel, but the kids remain - remnants of her, and so naturally they belong to him.
Good End Drift AU
Dipper is devastated by losing Mabel - it might not be worse than in regular fwtb, but there’s a bit more piled on there, what with being separated from her for all those years, walking the knife’s edge between growing in power and keeping himself, and then only getting a few brief years with her before she’s lost again - for good this time.
But in this version, Henry would trust him. Dipper’s softer, more careful about his demonic nature. He makes more of an effort to be a good person in every way, because that’s all he has to stave off what he’s become. Friend-marriage for tax benefits is far likelier in this version, and they’d be able to mutually support each other in raising the kids and dealing with their grief over losing Mabel.
