In essence, the Old Gods were parasites. Once they had burrowed too deeply into their host, forcibly removing them would kill the host as well. This had already been proven when Aman'Thul uprooted the strongest Old God, Seven-Headed Y'Shaarj. That reckless attack had torn a wound in Azeroth's surface that nearly killed Elune, and the danger left by that wound had not healed even today, hundreds of thousands of years later.
One lesson from the Well of Eternity was enough. Thus, before leaving, the Titans had forged prisons for the remaining three Old Gods from which they could never escape, for all eternity. It was just as Dick had realized when facing C'Thun: these prisons did not stand in the world in any way mortal beings could imagine. They bound the Old Gods on a higher plane. As long as those disgusting parasites refused to relinquish the world source they had corrupted, they could never emerge from their prisons. And once they relinquished it, the mightiest servants the Titans had left on Azeroth could kill them without harming the world!
That was how C'Thun had died, but Yogg-Saron's situation was clearly more troublesome.
He had broken out earlier than C'Thun. Ulduar's peculiar circumstances prevented him from corrupting the world again, but over those tens of thousands of years, he had recovered from his weakened state and regained his greatest strength. He was more cautious and more cunning than C'Thun. Even C'Thun's escape a few years earlier had borne traces of his involvement behind the scenes.
This was a truly dangerous being. Dick was certain that once he broke free of Ulduar's prison, this world's fall would be imminent. Of course, the likeliest outcome was that the moment Yogg-Saron stepped out of Ulduar, the Creators at the Forge of Origination would