[Fingolfin II]

Some good ideas Dûrbelethwen, but I disagree with your theory. Let me say why:

Another point (though I admit a shaky one) is why would Bilbo and Sam sail to the Undying lands late in life if they were going to die soon anyway. Particularly Bilbo for I do not see a reason why he could have not died in Rivendell, I am sure the remaining Elves there would have given him a very nice funeral.

As well as the reasons given by Rinfanawen, Bilbo and Sam had suffered a lot- they both bore the Ring, albeit Sam only bore it for a very short time. They felt it's effects (Bilbo became very attached to the Ring and Sam saw himself as the 'conquering gardener' in the world) and were thus permitted to travel to Tol Eressea. The Undying Lands were a 'paradise' away from Middle-Earth and a resting place for both immortals and mortals like Frodo, Sam, Bilbo and Gimli.

Frodo was sent or allowed to pass over Sea to heal him if that could be done, before he died. He would have eventually to 'pass away': no mortal could, or can, abide for ever on earth, or within Time. So he went both to a purgatory and to a reward, for a while: a period of reflection and peace and a gaining of a truer understanding of his position in littleness and in greatness, spent still in Time amid the natural beauty of 'Arda Unmarred', the Earth unspoiled by evil.- The Letters of J.R.R. Tolkien, 246

Dûrbelethwen, you said-

In one of the letters Professor Tolkien clearly states that Tuor was given elf immortality just as Luthian was given human mortality.

Tuor was given elven immortality because of his love of the Noldor and his services to Ulmo. However, this does not necessarily mean that the Hobbits and Gimli will be given immortality just because they inhabit the Undying Lands. In the Akallabeth, somewhere I recall that the messengers of Manwe said that even if the Numenoreans lived in Valinor, they would die the quicker like 'moths exposed to a light too bright' or something along those lines. In short, Tuor was a special case and Tolkien himself said that Frodo, Sam, Gimli and Bilbo would die-

I have said nothing about it in this book, but the mythical idea underlying is that for mortals, since their 'kind' cannot be changed for ever, this is strictly only a temporary reward: a healing and redress of suffering. They cannot abide for ever, and though they cannot return to mortal earth, they can and will 'die' of free will, and leave the world.- The Letters of J.R.R. Tolkien, 154

This quote above is the next part of the letter which you used as an example and I believe, proves my point about Tuor being a special case.

Also-

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.- The Letters of J.R.R. Tolkien, 325

That seems pretty conclusive to me. Thanks to Legolas' FAQ Article, which provided me with the quotes from Tolkien's letters, so that I didn't have to look them up myself .

A final point is in the appendice the Tale of Aragorn and Arwen. At the end of his life Aragorn told Arwen to leave for the Undying Lands now that would soon be dead. It would be safe to assume this is because he wanted her to take back her immortality.

Arwen was also another 'special case'. She and her brothers had the choice of mortality or immortality because of their descent through Elrond's side. She chose mortality on Cerin Amroth, but after Aragorn died she had the chance to repent as you said, and take back her immortality. However, if she went Valinor, she wouldn't be able to come back and be mortal- she couldn't chop and change. As she said, her 'choice was made long ago' and the gift of going to the Undying Lands she gave to Frodo. So, Arwen had a choice- she was a special case. She chose mortality and died.