“In any case a confrontation of Frodo and Sauron would soon have taken place, if the Ring was

“In any case a confrontation of Frodo and Sauron would soon have taken place, if the Ring was intact. Its result was inevitable. Frodo would have been utterly overthrown: crushed to dust, or preserved in torment as a gibbering slave. Sauron would not have feared the Ring! It was his own and under his will. Even from afar he had an effect upon it, to make it work for its return to himself. In his actual presence none but very few of equal stature could have hoped to withhold it from him. Of ‘mortals’ no one, not even Aragorn. In the contest with the Palantír Aragorn was the rightful owner. Also the contest took place at a distance, and in a tale which allows the incarnation of great spirits in a physical and destructible form their power must be far greater when actually physically present. Sauron should be thought of as very terrible. The form that he took was that of a man of more than human stature, but not gigantic. In his earlier incarnation he was able to veil his power (as Gandalf did) and could appear as a commanding figure of great strength of body and supremely royal demeanor and countenance.

Of the others only Gandalf might be expected to master him—being an emissary of the Powers and a creature of the same order, an immortal spirit taking a visible physical form. … [However, c]onfrontation of Sauron alone, unaided, self to self was not contemplated. One can imagine a scene in which Gandalf, say, was placed in such a position. It would be a delicate balance. On one side the true allegiance of the Ring to Sauron; on the other the superior strength because Sauron was not actually in possession, and perhaps also because he was weakened by long corruption and expenditure of will in dominating inferiors. If Gandalf proved the victor, the result would have been for Sauron the same as the destruction of the Ring; for him it would have been destroyed, taken from him for ever. But the Ring and all its works would have endured. It would have been the master in the end.“

—J.R.R. Tolkien, The Letters of J.R.R. Tolkien, ”246” (What would have happened in a confrontation with Sauron if Frodo or Gandalf had taken the Ring)