"As for Frodo or other mortals, they could only dwell in Aman for a limited time — whether brief or long. The Valar had neither the power nor the right to confer ‘immortality’ upon them. Their sojourn was a ‘purgatory’, but one of peace and healing and they would eventually pass away (die at their own desire and of free will) to destinations of which the Elves knew nothing."
J.R.R. Tolkien, Letters, #325
"Frodo in the tale actually takes the Ring and claims it, and certainly he too would have had a clear vision — but he was not given any time: he was immediately attacked by Gollum. When Sauron was aware of the seizure of the Ring his one hope was in its power: that the claimant would be unable to relinquish it until Sauron had time to deal with him. Frodo too would then probably, if not attacked, have had to take the same way: cast himself with the Ring into the abyss. If not he would of course have completely failed. It is an interesting problem: how Sauron would have acted or the claimant have resisted. Sauron sent at once the Ringwraiths. They were naturally fully instructed, and in no way deceived as to the real lordship of the Ring. The wearer would not be invisible to them, but the reverse; and the more vulnerable to their weapons. But the situation was now different to that under Weathertop, where Frodo acted merely in fear and wished only to use (in vain) the Ring’s subsidiary power of conferring invisibility. He had grown since then. Would they have been immune from its power if he claimed it as an instrument of command and domination?
Not wholly. I do not think they could have attacked him with violence, nor laid hold upon him or taken him captive; they would have obeyed or feigned to obey any minor commands of his that did not interfere with their errand — laid upon them by Sauron, who still through their nine rings (which he held) had primary control of their wills. That errand was to remove Frodo from the Crack. Once he lost the power or opportunity to destroy the Ring, the end could not be in doubt — saving help from outside, which was hardly even remotely possible.
Frodo had become a considerable person, but of a special kind: in spiritual enlargement rather than in increase of physical or mental power; his will was much stronger than it had been, but so far it had been exercised in resisting not using the Ring and with the object of destroying it. He needed time, much time, before he could control the Ring or (which in such a case is the same) before it could control him; before his will and arrogance could grow to a stature in which he could dominate other major hostile wills. Even so for a long time his acts and commands would still have to seem ‘good’ to him, to be for the benefit of others beside himself.
The situation as between Frodo with the Ring and the Eight* might be compared to that of a small brave man armed with a devastating weapon, faced by eight savage warriors of great strength and agility armed with poisoned blades. The man’s weakness was that he did not know how to use his weapon yet; and he was by temperament and training averse to violence. Their weakness that the man’s weapon was a thing that filled them with fear as an object of terror in their religious cult, by which they had been conditioned to treat one who wielded it with servility. I think they would have shown ‘servility’. They would have greeted Frodo as ‘Lord’. With fair speeches they would have induced him to leave the Sammath Naur – for instance ‘to look upon his new kingdom, and behold afar with his new sight the abode of power that he must now claim and turn to his own purposes’. Once outside the chamber while he was gazing some of them would have destroyed the entrance. Frodo would by then probably have been already too enmeshed in great plans of reformed rule — like but far greater and wider than the vision that tempted Sam (III 177)5 — to heed this. But if he still preserved some sanity and partly understood the significance of it, so that he refused now to go with them to Barad-dûr, they would simply have waited. Until Sauron himself came. 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.
* The Witch-king had been reduced to impotence.
5 ‘Wild fantasies arose in his mind; and he saw Samwise the Strong, Hero of the Age, striding with a sword across the darkened land, and armies flocking to his call as he marched to the overthrow of Barad-dûr.’"
J.R.R. Tolkien, Letters, #246
"Sam was cocksure, and deep down a little conceited; but his conceit had been transformed by his devotion to Frodo. He did not think of himself as heroic or even brave, or in any way admirable — except in his service and loyalty to his master. That had an ingredient (probably inevitable) of pride and possessiveness: it is difficult to exclude it from the devotion of those who perform such service. In any case it prevented him from fully understanding the master that he loved, and from following him in his gradual education to the nobility of service to the unlovable and of perception of damaged good in the corrupt. He plainly did not fully understand Frodo’s motives or his distress in the incident of the Forbidden Pool. If he had understood better what was going on between Frodo and Gollum, things might have turned out differently in the end. For me perhaps the most tragic moment in the Tale comes in II 323 ff. when Sam fails to note the complete change in Gollum’s tone and aspect. ‘Nothing, nothing’, said Gollum softly. ‘Nice master!’. His repentance is blighted and all Frodo’s pity is (in a sense*) wasted. Shelob’s lair became inevitable.
This is due of course to the ‘logic of the story’. Sam could hardly have acted differently. (He did reach the point of pity at last (III 221-222)4 but for the good of Gollum too late.) If he had, what could then have happened? The course of the entry into Mordor and the struggle to reach Mount Doom would have been different, and so would the ending. The interest would have shifted to Gollum, I think, and the battle that would have gone on between his repentance and his new love on one side and the Ring. Though the love would have been strengthened daily it could not have wrested the mastery from the Ring. I think that in some queer twisted and pitiable way Gollum would have tried (not maybe with conscious design) to satisfy both. Certainly at some point not long before the end he would have stolen the Ring or taken it by violence (as he does in the actual Tale). But ‘possession’ satisfied, I think he would then have sacrificed himself for Frodo’s sake and have voluntarily cast himself into the fiery abyss.
I think that an effect of his partial regeneration by love would have been a clearer vision when he claimed the Ring. He would have perceived the evil of Sauron, and suddenly realized that he could not use the Ring and had not the strength or stature to keep it in Sauron’s despite: the only way to keep it and hurt Sauron was to destroy it and himself together — and in a flash he may have seen that this would also be the greatest service to Frodo.
* In the sense that ‘pity’ to be a true virtue must be directed to the good of its object. It is empty if it is exercised only to keep oneself ‘clean’, free from hate or the actual doing of injustice, though this is also a good motive.
4 ‘His mind was hot with wrath…..It would be just to slay this treacherous, murderous creature…..But deep in his heart there was something that restrained him: he could not strike this thing lying in the dust, forlorn, ruinous, utterly wretched.’"
J.R.R. Tolkien, Letters, #246