Sauron should have won!

[The Saucepan Man]

If that happened, the new possessor could (if sufficiently strong and heroic by nature) challenge Sauron, become master of all that he had learned or done since the making of the One Ring, and so overthrow him and usurp his place.

Even then, Sauron would have won, for the new bearer would have become corrupted by the Ring which was itself a part of Sauron. And, while that new bearer might be able to master the Ring sufficiently at first to usurp Sauron, he or she would surely eventually become subservient to its will. And then, assuming that it remained intact, Sauron would be able to return and reclaim it. The Ring, no doubt, would be only to glad to help him do so, and so the new bearer would not be able to rely on its power.