Magic vs. Science

I had an idea to mix science and fantasy together for my open table of Keep on the Borderlands. The following is a basic concept. It still needs some work and may be too far out there for traditionalist, but it does excite me with the possibilities.

Imagine your typical fantasy medieval world in which the typical Dungeons & Dragons campaign takes place. In a fertile region of the world a massive city populated by the “civilized” races, humans, dwarves, elves and so forth go about their business under the watchful eye of powerful noble families. The city is locked in a horrible war with a vile Necromancer King in the Wastelands to the North. The Forces of “Light” are beginning to despair as the tide of the war has taken a drastic turn in the favor of “Dark”.
 Then without warning from the heavens above a massive celestial object smashes into the city. In the aftermath of the destruction it’s learned that a similar fate occurred to the Necromancer’s vile city of Evil. A new threat has emerged. A plethora of “Demons” from the sky, some who look remarkably human and others that could just be considered to be another kind of monster in this world’s ecology begin to subjugate and enslave all people of the surrounding lands regardless of their allegiance to the Light or Dark. They bring new weapons of star metal and a magical power they call “Science”. They fear and don’t understand the “Magic” that perfuses the planet and begin a pogrom against magic users and their ilk.
 Today, enclaves of the “Good” Races band together and continue to fight against the Necromancer and the new Demonic threat that besieges the planet. Daring raids are made into the destroyed city to recover lost magical treasures as well as attacks on the outposts of the Invaders who continue to study and enslave the native population.