Estou enviando aqui uma parte relevante de um tópico do fórum sobre a imortalidade dos mortais que passam para Terras Imortais. Parece que Christopher Tolkien usou muitas das cartas de seu pai para acumular um bom corpo de conhecimento sobre a Terra Média e suas regras no O Silmarillion , mas que algumas cartas específicas para a vida e morte de Frodo e Bilbo Baggins não estavam claras, (talvez intencionalmente - minha interpretação - O tópico inteiro é uma leitura muito interessante).
Aqui está a passagem relevante que encontrei:
But in this story it is supposed that there may be certain rare exceptions or accommodations (legitimately supposed? there always seem to be exceptions); and so certain 'mortals', who have played some great part in Elvish affairs, may pass with the Elves to Elvenhome. Thus Frodo (by the express gift of Arwen) and Bilbo, and eventually Sam (as adumbrated by Frodo); and as a unique exception Gimli the Dwarf, as a friend of Legolas and 'servant' of Galadriel.
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. - Letter #154
Ou da carta # 325:
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 sojorn 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.