[Mithadan]

In one of his Letters, Tolkien speculates on what might have happened if Gollum had failed to wrest the Ring from Frodo and fall into the fires. He suggests that Sam would not have the will or the heart to kill his master. The Ringwraiths would have been summoned to Orodruin. Frodo would not have had the time to learn how to control the Ring nor the strength to truly master it. The Wraiths, nonetheless, would not have been able to assault him. Rather, they would feign obedience and invite him to survey his kingdom. Once Frodo had left the Cracks of Doom, they would have contrived to seal the entrance and either Sauron would have come to seize the Ring or the Wraiths would have carried him to Barad Dur.

I do not think that anyone could destroy the Ring after possessing it as long as Frodo did. This is why the Fellowship was formed; to provide him with assistance to carry the Ring to its destination and to help him marshal the will to destroy it or to do so on his behalf. Whether they would have succeeded is another story. For this reason, I have several times argued that Frodo did not fail in his quest. He did as much as could have possibly been done and perhaps no one else could have done as much. To destroy the Ring was beyond his capacity and would have likely been impossible for anyone who had possessed it for any length of time.