[Mänwe]

Lindil you raise an interesting point, though I would dare to correct you and say that it was indeed Gandalf who discovered the mind and plans of Saruman before any. I say this on the existence of the following quote;

“…and the valley below seems far away. I looked on it and saw that, whereas it had once been green and fair, it was now filled with pits and forges. Wolves and orcs were housed in Isengard, for Saruman was mustering a great force on his own account, in rivalry of Sauron and not in his service yet.” – (Chapter 2, The Council of Elrond)

There is no text before hand suggesting that the Ents had discovered the intentions of Saruman before this quote and so it is I believe unfounded to say that it was they who discovered it.

Why no-one else should have discovered the truth behind Saruman before Gandalf bought such tidings to the council in Rivendell was I believe the turmoil of the times, and the numerous references to Saruman having masked his feelings well.

“So Saruman guessed, and he had concealed his mind and deceived his messenger…” (Book II Chapter 2, The Council of Elrond)

“…and I still trusted the lore of Saruman” (Book I, Chapter 2, The Shadow of the Past)

“`This is grievous news concerning Saruman,' he said; `for we trusted him and he is deep in all our counsels.” (Book II Chapter 2, The Council of Elrond)

The elves still held him in high regard and had no reason to distrust him; consequently they would not have watched him. Gandalf also the most prominent (other than Saruman) of his order at this time still trusted him.

“all that he would reveal to us of his ring-lore told against my fears. So my doubt slept - but uneasily. Still I watched and I waited.” (Book I, Chapter 2, The Shadow of the Past)

“But Saruman has long studied the arts of the Enemy himself, and thus we have often been able to forestall him. It was by the devices of Saruman that we drove him from Dol Guldur. It might be that he had found some weapons that would drive back the Nine.” (Book II, Chapter 2, The Council of Elrond)

Though this trust was beginning to become more uneasy until his meeting with him at Orthanc after the news bought to him by Radagast. In summary he had deceived them all, and none had known his real thoughts. The absence of a discovery before the point at which Gandalf saw, is proof of this I think.

As for what might have happened, I am not a great fan of speculation but perhaps we would see a “re-run” of the flight of Sauron from Dol Guldur. The Council perhaps may have driven Saruman from Orthanc.