[Lalwendë]

It's not entirely clear exactly what made Saruman go 'bad'. It could have been looking in the Palantir, it could have been his lust for the Ring. It could simply have been his proud nature. Either way, one thing caused him to reach that point and I think that this was his thirst for Ring Lore, which he came to regard as all-important in his own way of approaching the mission he had been set.

In contrast, Gandalf went out into the world and mixed with the people, and in this way he learned of what the Ring could do, and he also learned of its whereabouts. Saruman just learned as much Ring Lore as he could and retreated to Orthanc trusting that information would come to him.

Anyway, this is a roundabout way of getting to the point. I think that if Saruman had by chance not gone 'bad', his Ring Lore would have been the downfall of Middle-earth. Of course the Ring would have found its way to him as the others on the White Council would have deferred to his impressive knowledge and sought his advice and help. Even if Gandalf and Galadriel would have refused to touch the Ring, I think Saruman would not have resisted; his 'knowledge' would have deceived him and he would have attempted to deal with it. And there he would have been caught.