[DnD 4.0] Plot thoughts

[Ceaon]

...murdered out...

Dutch too, right?

First of, you have a lot of potential with wars between guilds and against the drow before you even start informing the PCs of the history of the King.
Start of with a big battle against the drow in which the PCs can distinguish themselves from the rabble.

Now, you have the guild of the PCs. Let them join by choice, or have them be members from the start. It should appear to be good on the outside, but contain evil (at least some evil) within. This way, you almost guarantee the PCs will eventually break with their guild. That is, if they're good.

You'd have another guild that is obviously evil, so the PCs have some humanoids they can slaughter without feeling remorse. Add some guilds who can be played out against eachother, with some good and some evil members so the PCs don't know exactly who to trust. You might add the vampire as a recurring enemy or unexpected help in some of these quests so you can make it to be that he's the Big Bad or something.

Then, just when the PCs are on the winning hand, make sure they are the ones to discover about the King and his history. Making this discovery is a quest on its own. Now the PCs must choose what to do. From here on, make sure that whichever side the PCs choose, that side will eventually win, but it will be at a disadvantage.

Add a quest to retrieve the King's equipment, or to purify to King's ghost, or to find the King's forgotten heir. Make sure the leaders of the different guilds all play a different and important role: let them all have a key item or key information imporant to the PCs victory.

And of course, the guild the PCs started with will be out for revenge and may even have the Big Bad as a member/leader.

Hope this helps.