Overview:
[sblock]From the adventure (well, with a few changes to update it):
Darius was standing watch, along with two other guards – Dimha and Lein – when Lein suddenly fell over, his throat slashed open. For an instant Darius saw a swarthy half-elf man holding a black scimitar and striding in plain sight, but then he vanished as shadows wrapped around him like a cloak. The door to the room burst open, and a bladed whip lashed out, held by a beautiful dark elf woman with violet hair. The whip snared Darius by his throat, and the woman tugged him through the doorway, where she grabbed him and delivered a poisoned kiss. He cried out to sound the alarm, and guards in the main hall responded, but a third assassin – a white-haired dark elf woman with a double sword – held them off.
Darius remembers the world bending around him, and as he stumbled back into the room, shadows moved past him and Dimha fell too. Paralysis and hallucination gripped Darius, and he shivered on the floor, unable to stop the assassins as they carried away the body of his emperor, Drakus Coaltongue. Then firelight blinded him, and the entire world heaved around him. He recognized the power in the air, and he knew the Torch had been activated.
Three elite bodyguards (Darius, a cleric; the other two fighters) defended Coaltongue, standing in the castle's throne room while the emperor slept in the room behind it. The magic of that room was such that no one inside the room could take any hostile action unless the castle's rightful lord sat on the throne and gave them permission, and no monsters or other nasties could enter.
A half-elf shadowdancer assassin named Rhuarc snuck inside the room and hid in plain sight, originally intending just to unlock the door and disable some wards. But before going to bed, Coaltongue casually said to his three bodyguards something like, "I'm not sure how this magic works, so just in case, all of you are free to fight." Even though Rhuarc was hidden, the blanket permission applied to him, so he was able to make the first strike.
Quillathe, the drow with the whip, attacked from outside the room and pulled Darius through the doorway, so she could poison him. (She can generate her own poison.) Yvonnel, the second drow, just held off the mundane guards.
The poison left Darius delirious, and when the drow activated the Torch, they did it wrong, causing the upper section of the bunker-like Castle Korstull to be partially pulled into the . . . well, this will probably change with the new 4e cosmology, but it was in the liminal space between the plane of fire and the astral plane. And in 3e cosmology, people don't age in the Astral Plane, or heal naturally.
So Darius survives, safe in his room while the rest of the castle is overrun with undead. In his fevered state he scrawls prophetic passages on the stone floor of the throne room, but he can never die of hunger or thirst, and never heal of his poisoned injuries, so he simply lies there until the PCs (who aren't undead, and thus can enter the room freely) find him.
So I don't think a player-run cut scene would work so well, because, well, the key players get assassinated or left for dead pretty early on. You might let them play the assassins, if you want, though that could get dicey with setting the right mood, since Rhuarc, at least, is supposed to come across as sort of a bad-ass when the heroes finally do meet him.
I dunno. Maybe they could play more mundane guards, the folks who get cut down as the assassins make their exit. But really, if you don't have the layout of the castle yet, probably your best bet is use some other event for a flashback. Maybe they play soldiers sacking a city, and they teleport in with Coaltongue and fight alongside him and Shaaladel against Syana, a gold dragon who is defending the place.
Syana, or her skeleton at least, is mounted as a trophy in Castle Korstull.[/sblock]