This is a crossover with one of Gerry Anderson's TV shows (named at the end). All characters and settings belong to their respective creators, this story may not be distributed on a profit-making basis.
By Marcus L. Rowland
What was asked is simple; granting it will not be. No ordinary Justice Demon could come close, but D'Hoffryn is taking a personal interest. There's no simple path to what was asked, not in the here and now, but go back a few decades, tweak things here and there, and hey presto!
In the seventies a NASA engineer working on nuclear rocket propulsion is inspired to write two extra equations. The implications are staggering, a twenty-fold increase in power and reliability. Development won't be cheap, but the civilian applications and potential industrial spinoff justify development. Billions go into the space program (starved of funds, dozens of social and medical programs wither and die. When the HIV epidemic arrives it will take decades to begin to develop treatments).
In 1985 the first of the new breed of nuclear reactors goes live, on Earth and in space. Even more powerful than theory has predicted, the gateway to the planets is opened. Admittedly they produce incredibly dangerous wastes (the crater at Three Mile Island and subsequent leukemia epidemic testify to that a few years later), but there's an easy fix - the new engines can lift anything into space, mass is no longer an issue. Ship everything up to the moon, it'll be safe there. The scientific base there can monitor things and make sure nothing goes wrong. It will take a few years to get everything ready, of course, meanwhile a 35% rise in cancer deaths is acceptable.
The nuclear waste dump opens in 1999. Monitored from Moonbase Alpha, all goes well at first. But towards the end of 1999 the engineers notice increasing instability. Within hours the dump starts to explode in a sustained reaction that drives the Moon out of its orbit and in towards Earth (tidal waves sweep the Indian ocean and drown more than half a million; thousands of species face extinction as they try to adapt to disrupted natural cycles) then out into space. Accelerating insanely fast, the Moon rapidly recedes towards the stars, vanishing as it finally crosses the light barrier.
Willow doesn't even notice. Wrapped in her grief, it will take several days for the implications of the Moon's departure to sink in. En route to Tibet, Oz gets the idea a little faster, and decides to head home. After all, from now on there's no need to worry about anything happening at the full moon...
Crossover with Space 1999, of course. I've taken mild liberties with the timeline - in Space 1999 the Moon left its orbit in September 1999, Willow's encounter with D'Hoffryn was at the end of November 1999.