I like it! Although I do have some nitpicks.
There are two typos: "deathbead" and "compells" instead of deathbed and compels.
If you don't buy the sword, Wilbur should still have it. But if you kill him while he's walking away, he doesn't have it, and if you kill him a minute later, when he's inside the house, he doesn't have it. Also, he has a Scimitar+1 inside, but not outside. It would be simple to tack on a simple CreateItem, to increase the odds of meeting the Marilith.
Upon meeting the Marilith (cool name, BTW), the player has multiple conversation options to mention the Red Scimitar, even though (s)he has no reason to suspect that that weapon is what she wants.
The Cowls DD in rather quickly--I expect that even if the party immediately used Breach, they still wouldn't be able to dispatch her before taking the Rep hit. I would wait for about 7 rounds before the Cowls show up. And when they do, have them initiate conversation with the nearest party member and publicly blame them for the disturbance, just before they leave.