Three unrelated things that bug me about the keep

[That Man]

Just some facts ...

Glaicas ... the enchantment can be broken (after installing a bug fix). He tells us that a snakelike being (Yuan-Ti) charmed him.
Also Nalia comments on seeing him again: "Oh my god, Glaicas! Why are you attacking? It must be some charming magic about you!"

Then, there are no bodies except the servant's because the guards have mostly been bribed into leaving. Tor'Gal says this himself.
And there are enough bodies ... from the servants who weren't important enough to being bribed. They get killed before the party's very eyes.
 

Here's a thought, it could have been a Marilith Tanar'ri.  They are the tacticians of the Tanar'ri, so figuring out how to conquer the keep would be child's play.  They have powerful magic and physical skills, so one could dominate Torgal and all his back with ease.  They are half snake, half six armed woman, so that fits Glaicis' description.  Finally, Being a demon, Roenall or whoever could have just summoned the Marilith to take the keep and then dismissed her when the job was done.

If it was done this way, Togal or Delcia probably never even knew who ordered the attack, and a summoned fiend is hardly a credible witness, so the Roenalls' would be safe from scrutiny there.

One quest could be haveing Delcia or Glaicis (if you break his charm) give a hint about this, and then a quest to find a way to summon the Marilith (either by finding her true name or by using an aritifact or scroll espically attuned to her) and question her about who her master was.

Having a true Tanar'ri prowling about could also expain why so many "loyal" servants ran for the hills.

[That Man]

Well I'd look at motive. Suppose (hypothetically) that the Roenalls were the ones who incited the attack. What do they gain?
Ideally, Nalia marries and they get control of the keep. A war-torn, highly damaged keep in need of much rebuilding.
Now to propose an alternative - suppose they wait until AFTER Nalia marries Isaea (according to the storyline as I understand it, that was bound to happen fairly soon anyways, despite any attempts at meddling, if Lord Roenall had to continue to maintain respect amongst the nobility in order to maintain his lands). In that case, if they launch the same attack on the keep they are GUARANTEED that they'll get control if Lord De'Arnise dies.
To propose another point - why attack at all? They want the keep, preferably as intact as possible. All it takes is one good assassin to give them that, if they wait until Nalia is married.
Further, the Roenalls may be scum but they aren't supposed to be stupid. If I were planning such an attack, I'd arrange to take Nalia into "protective custody" just before the trolls struck or as they struck a: to ensure that she didn't get killed, and b: to ensure that she didn't go against their wishes.

Further, they value their nobility and family prestige highly. While they don't have a problem with being involved in dubious practices (e.g., slavery), they risk a whole lot more if they arrange for a band of maurading trolls to go cross-country from who knows where, march into the keep on their word, kill the local lord, and take over. The cost there if they are somehow caught, I'd think, is higher than would be in their interest.

So the next question is who could gain out of the attack on the keep.
The Rakshasa could have a motive (in that they might want the Flail of Ages in circulation again), but I don't think the attack is in their style (they'd go take it themselves, and then just send it out again once they had it).
Lord Roenall was supposed to be ruling over a time of great prosperity in his land, which could encite either jealousy or fear from other lords.
It's possible that it was simply someone angry with Lord Roenall (a foe he defeated before he settled down to rule?), seeking revenge.
It could have been the first move on the part of someone with designs of conquest to create some unrest before revealing him/herself. A noble, upstanding lord with a sound keep and loyal guards would be a good first victim.
Or it could have been a move to deny the Roenalls the keep (if it's ruled by trolls, then it isn't ruled by the Roenalls), which brings in all the enemies of the Roenalls.
And yes, I know that the Roenalls almost got it sooner as a result, but it could seem doubtful that a group of adventurers would just happen to wander by, be recruited, and be strong enough to drive out tor'gal and his fast-mending minions.

The thing you have to tie it back to is the slaver quest.  Am I the only one who noticed that the mind flayer enclave is directly beneath the slaver compound in the temple district?  Or that the Hidden (who is revealed to be a mind flayer for no reason) seems to hang out in the area controlled by the salvers in the slums?  Then there is the question of why Firkraag would have the only key to get into the mind flayer enclave.

It could be a conspiracy to set up a steady supply of slaves (like a reverse of the underground railroad) and the de'Arnise keep was a piviotal point in the scheme.  Firkraag could have simply seen it as a means of getting some extra cash and not cared about it beyond that.  The Mind Flayers would have seen it as an easy way to get meals.  The Roenalls and Rakasha's could simply be red herrings to throw the party off, much like the runaround in the Umar Hills quest.

If you were feeling really ambitious, you could connect the Rakasha's, Firkraag, the Roenall's and the troubles in Trademeet all together.

Hmmm, now I have plot bunny for a fic.

[Who Was I?]

Thread necromancy!

Back on unrelated things bugging me about the keep, which for the moment happens to be this little bit:

THE de'ARNISE KEEP HAS BEEN INVADED
Captain Arat has said that he and his men will draw off as many of the enemy as they can if I can but open the drawbridge. The wheel to open the bridge will most likely lie on the keep's wall directly above the bridge.

Or rather the discussion leading up to that entry being placed in your Journal. (Sorry, can't remember the exact dialogue just now.) I'm always annoyed by Captain Arat's obvious lack of knowledge about the keep he's supposedly guarding -- the man isn't even sure of the location of the drawbridge's opening mechanism... Small wonder then that he's out of a job once the keep is liberated 

(And yeah, forgot my name and password so... guest posting it is.)

[nurgles_herald]

A still unrelated thing that bugged me- the servants had no scripting for what to do if you actually saved them!  And it is possible, by the way.  Open a door to a room with a servant and troll in it, but don't go in.  Cast any summon monster spell inside the room.  The troll will assault your summoned buddy, but leave the servant alone.  Kill the troll, and walk on in.  The servant is fine and dandy.  Note, though, that if you ever "see" the servant while the troll is still alive and well, he'll beeline for the servant.  But I've done a run through the keep and saved every single servant- game functioned exactly the same.  That sorta bugged me.

[Porthas]

Yeah there are a lot of  gotcha's in the game (like the saving the servants not resulting in any interesting outcome) because they really did rush it coming out.  Hence all the mods that not only add to the game but actually "fix" it.  I've read the bug fix list and it's gigantic.

[AndrewRogue]

To be fair, given the means it takes to save the servants, it seems like they probably weren't meant to be saved.