This should clear your doubts: http://db.mmo-champion.com/c/37813/deathbringer-saurfang/

I see Bolvar's name come up a lot with regards to finding him in the citidel as a Death Knight. My question is why? Perhaps I interpreted the Wrathgate video incorrectly, but Bolvar's dead man. We see Arthas take Saurfang's soul after he kills him, but Bolvar is hit with the undead plague and gets his face melted. Arthas left him alone.

No, it's just makes since that Saurfang is the only one with a chance to come back under Arthas's control, and the datamining seems to back that up.

There is a dialogue between Korialstrasz and Alexstrasza after the Wrathgate event. It goes as follows:

Korialstrasz says: My Queen, do they know?
Alexstrasza the Life-Binder says: No, my beloved.
Alexstrasza the Life-Binder says: [Draconic] Ashj zila gul kirasath lok ante il lok buras danashj Gul gul
Korialstrasz nods.
Korialstrasz says: They will not.
Alexstrasza whispers: Come to me,

This is the dialogue you see when Alexstrasza is talking to Korialstrasz but due to a bug where some players can speak Draconic, some players are able to read and translate the line of text that Alexstrasza says.

The line of text reads:

Alexstrasza: [Draconic] They must not discover the fate of the young paladin. Not yet.

(from WoWWiki)

Plus in the Yogg-Saron encounter you witness the Lich King trying to turn a human "Immolated Champion", suggesting that Bolvar at least sort of survived being roasted.

Welll... damn. I was really hoping it was the black knight. Again.

That is rather interesting... I didn't know all that. Still, I think there may be more to it. The cut scene clearly showed Arthas take Saurfang's soul, but they were attacked before he could get Bolvar's. Also, Arthas has already left the scene before Bolvar actually dies. To me this suggests that whatever happened, what Alexstraza is trying to protect us from discovering, has to do with Bolvar's contamination from the Plague.

The Yogg Saron event does seem complicate that theory. Unless what we see with Yogg is something else entirely. If you've read Arthas: Rise of the Lich King, there are recurring scenes with Arthas next to an Orc and a Human boy that whom is sick. I suppose it would be a bit of a stretch to say that this is what we see with the Yogg Saron encounter.

The Warcraft 2 death knights (like Teron Gorefiend) were orc souls in dead human bodies. The Lich King has Saurfang's spirit, Bolvar's corpse, and Ner'zhul's memories. And there you have it.

The plague used to kill Bolvar wasnt an undead plague. It was the plague designed by Putress to kill Undead and the Living alike. It has no further side effects other than killing. You don't rise afterward.

Wrath Gate was just a set back...

Sounds to me that "Deathbringer Saurfang" will be an old-school Death Knight, as in an orc's soul inside a human's body, combining themselves in one entity, like the ones that were created in the second war.

Seeing that Arthas absorbed Saurfang's soul into Frostmourne, and Bolvar's body was never found, It's a good bet that this is what happened.

Ps: What is it with Blizzard with all the [Noun]-bringers? Lightbringer, Ashbringer, Plaguebringer...

We'll definitely see Bolvar in 3.3. just look at the conversation between Alexstraza and Korialstraz.
To Gboyd: In "Arthas: rise of the lich king" that orc is probably Ner'zhul and the sick boy is Arthas himself.
As for everyone that says Arthas will make an old school DK, the point of the old school DKs were to combine the necromantic knowledge of the orc warlocks with the strength of the human warriors, Bolvar definitely has more knowledge than Saurfang Jr. so I can't see the point of putting Saurfang's soul in Bolvar's body.