okay so hear me out—there is a resolution to the "I love the human AU ending" and "oh god I miss our ineffable husbands so BAD" feelings.
After everything is done, and they've had the cottage in the south downs as many wonderful years as possible, at some point they'll both close their eyes for the last time.
...and open them on the desert of the Discworld.* For those who aren't aware, the desert (probably The Desert, tbh) is not the afterlife. It's a place in between, where Death brings souls that need to travel onward. For some, it's an easy stroll. For others it's an insurmountable passage, full of whatever torment they bring with them.
I think, for our angel and demon, it's a place to turn to each other and grin and say "Oh, that was a good one!"
I think after they die, they sit down on the edge of the desert and chat, and because they expect there to be wine and a picnic, there inevitably is wine and a picnic. For as long as they want, they gush to each other about how it went and their favorite parts, tease each other, argue, complain—and compare.
Because this isn't the first time they've done this.
And it isn't going to be the last.
I think once they're done talking, Death will approach. He tends to be lonely, so I think he enjoys these visits every century or so. They'll chat with him a bit, and eventually he will ask if they're ready to cross the desert.
They look at each other, and it's how they always look at each other. It's "to the world" and fingers pressed to lips pressed to lips; it's stargazing in the South Downs and a first date in the back of a neighborhood cafe.
Not looking away, Crowley says, "Nah," or maybe Aziraphale says, "Hm, not quite yet."
Either way Death nods, and takes out two convoluted hourglasses, with almost embarrassingly obvious angel and demon theming—and he tips them both over.
Aziraphale and Crowley both go up in waves of golden dust.
...and somewhere in the world, two humans are born, and the story begins again.
Because maybe our universe doesn't have magic—but that doesn't mean no universe does, and who said our souls have to stay here forever?
*This is inspired by this gorgeous comic by @hollow-head, which everyone should go look at and get teary-eyed over <3