There are a hundred ways I could react to your post, and, since my replies are, in fact, multiple, let us go in order:
1. First of all: ADAMIN! Welcome back! Long time no see, indeed! I confess I thought I would never have the pleasure to see you again. I’m glad to realise how wrong that supposition was. If this is your personal Christmas gift for us, I’ll accept it without any questioning
2. Thank you! I’m the happiest, if our stream of never-ending lore discussions managed to enthral you once more. Unfortunately, the thread has been suffering from a prolonged state of inactivity until now. It would lighten my heart to breathe a little bit of life in here, as it once used to be.
3. Well, I presume it’s time I took my teacher’s red pen in my hands and resumed the conversation, too.
They are sent to Mandos, where they are healed and granted a new physical body and if they wish can return to Valinor and reunite with their kin. So the Elves do not depart the world upon their death. This is specifically defined as the Destiny of Men, so this is an important uniqueness between the two.
Yes, that’s the fate that’s been assigned to the Elven race. I don’t quite recall having ever stated something which contradicted it. Some of the words I’m used to employing are maybe to blame: with ‘material world’, in its broadest sense, I often mean the material universe itself, where matter exists and whose laws govern it. Therefore, I refer to the realm of physical being, as opposed to the timeless and eternal dimension in which Eru has dwelling. Sometimes, however, with ‘world’ I more narrowly indicate Middle-earth and all the lands belonging to mortal territories, in opposition with the Undying Realms.
I reckon it’s seldom not so consistent a terminology
One big fascinating aspect of the Elves’ immortality is that it doesn’t really suit the common definition attached to the name. Perhaps, it would be more accurate to view it as extreme longevity, since their lives are inherently tied to Arda, and they shall live as long as the world does. Needless to say, Elves do encounter grief, very slow ageing, and, in the saddest case, physical death (either violent or caused by insurmountable distress), with the only difference being, in your words, that their souls are later gathered in Mandos, and, after a time and subject to there being the proper will to be revived, they are embodied again and granted the possibility of a happy existence in Aman. Nonetheless, time will always affect them at various degrees, with the response of each being dependent on the specific Elf and the happenings he or she came to endure (from the ever-young Galadriel, born under the majesty of the Two Trees, to the stern appearance of Círdan, who’s much older than her, spent his whole life in Middle-earth, and bears more evident traces of wear and fatigue).
Aside from the mentioned facts, it surely gets to be considered as immortality by the standards of common Men, who mainly associate their being immortal with the capability to resist death from old age. In other words, they’re all different nuances and angles from which to look at canons. The splendour of these books, in brief
