Ah yes, when the dire Prophecy you've set up early in the game comes back and is fulfilled despite all the best efforts of the PCs...

Actually, you can predict pretty much any dire thing and lay good odds on the PCs bringing it about in some way or another.

Transcript

R2-D2: Right, I'm off to the Peace Moon. There's no way I'm missing the first test firing. See you chumps later.
[SFX]: < doop ting bebedooby-bing boodoot bop whroooop bzzt bop squee dip >
{beat}
Obi-Wan: Anakin, you've destroyed and divided the Jedi Order. All to satisfy your own lust for power.
Obi-Wan: Palpatine believes you are a hero of the Republic, but I've seen through your deceptions.
Obi-Wan: Master Windu and Yoda warned us of the Prophecy.
Obi-Wan: Of the one who will bring Balance to the Force.
Obi-Wan: The midi-chlorians have made you unstable. I should have seen it long ago.
Obi-Wan: Good is now balanced by evil. Love is now balanced by death.
Obi-Wan: Death that you have wrought.
Anakin: I... I don't suppose you'd care to settle this with a Force Arm-Wrestle?