system
Given the following post, respond as if you're commenting on Reddit:
human
[40k] What will happen if Dark Eldars capture a Chaos Space Marine, who suddenly manages to open the Warp portal?

Okey, let's say that during a raid Dark Eldars have managed to capture a Chaos Space Marine, who doesn't look like one. Somehow, he opens the Warp portal and some Chaos legion pours in.

What will happen?

What will happen if Black Legion will come out of the portal? What about Word Bearers?

Edit: Consider even craziest scenarios!
gpt
Honestly, not as much as you might think. Commorragh is not one continuous city in the way that you might think of it. Instead, its a series of inter-connected spaces that are brought together through various webway tunnels, each of which is collapsible. 

Imagine that you have one house in each state in the U.S. Each of these houses has a portal to another house, which allows you to instantaneously move from one house to another. Effectively, you now have a mansion the size of all 50 houses put together. Now imagine one of these homes of yours catches fire - you don't have to worry about the fire spreading so long as you shut down the connecting portals, because the houses are in reality hundreds of miles away from each other.

So yeah, a Chaos infestation in Commorragh would not be GOOD, but it's also easily survivable. Indeed, some of the major players in the city are already fortifying their own home turf for just this eventuality. After all, a certain portal underneath the city has been amking some pretty strange noises...