It isn’t really a cinematic, so I can’t call it that, but you are given a one-use hearthstone to Tranquillen and told to meet Sylvanas at Windrunner Spire. When you do, you hear her and Nathanos, finally speaking in loving tones to each other as they part ways, and he says something rather scary. This part keeps getting left out of the transcript. She also says something after it that isn’t particularly informative but is still part of the whole thing. I put actions in square brackets.
Following is a transcription of the entire loyalist scene:
Nathanos: As do I Dark Lady, but when the time comes there can be no hesitation.
Sylvanas: There won’t be. Safe journey, Nathanos.
Nathanos: Safe journey, my love.
[Nathanos departs; Sylvanas turns to you and walks with you up the hill to Windrunner Spire, banshees in worshipful positions around her the whole way.]
Sylvanas: Ah, Champion! I wasn’t certain you made it out of Orgrimmar. If the traitors knew of your service to me, they’d have put you in irons…or worse. Saurfang’s ill-considered challenge may have ended the war prematurely, but it doesn’t matter now. Countless souls have been fed to the hungering darkness.
Sylvanas: Though I cared nothing for the living, I did pity the Forsaken. For the great injustice that made them what they are. I understand the cruelty of fate better than anyone.
[Sylvanas turns to look north over the coast of the Ghostlands.]
Sylvanas: But despite all I taught them, they stubbornly clung to hope. To life. They will learn the truth, along with all the rest. My bargain with Azshara will yet bear fruit. The armies of Azeroth will fight her master, and he will line their streets with corpses. In the end, he too will serve Death.
[Sylvanas turns to you and walks past you back down the hill.]
But enough reflection. There are preparations to be made.
[Sylvanas gets ready to depart.]
Sylvanas: Nothing lasts. When next you see me, you will understand.
After the little mini-not-really-a-cinematic and she disappears into the trees southeast towards the Thalassians (from Windrunner Spire where you meet her) she says just via chat bubble the following:
Sylvanas: Fate approaches, Champion. Be ready.