As you may recall, After the awakening of the Elves, Oromë was sent to bring them to Valinor. Some of the Elves refused to go, however, and were dubbed the Avari (the Unwilling), and they drifted off to forests and caves. Others started the trip but stayed behind without crossing the Misty Mountains; these basically became the Sindar. The Sindar, by and large, became the Silvan Elves, and they’re part of recorded history, while very little is ever really recorded about the Avari.
At the end of the Third Age, most of the Calaquendi (the Elves who did go to Valinor) depart for the West by ship, with a few stragglers following later. What happened, though, to the Silvan Elves and the Avari? Did they finally opt to go West? Would they have been allowed aboard the ships? Or are they still lurking in shadowy forests to this day?
Side question: When the Calaquendi are killed (in battle, say), their spirits go to the Halls of Mandos in Valinor, to rest, recharge, and get re-bodied. Nearly all of them then stay on in Valinor as opposed to returning to Middle-Earth. What happens to the Sindar or the Avari when they die, though? Do they wake up in Valinor, where they never wished to go?
We know of at least 1 Sindarian elf, Legolas, that went west. So it wasn’t restricted solely to Noldor. Then there is mention of Silvan elves traveling out of Lothlorien down the Anduin and eventually going over the sea in the second age.
As for the others, if I remember right, the Valar were basically required to ultimately offer the rehousing of elven spirits in bodies. Elven fea were immortal but to enjoy the world had to be housed in flesh. The Valar were empowered to do this. Since an elf is an elf, the Valar would have been required to rehouse all elven spirits that made themselves available.
So I can see some Avari spirits rejecting or fearing the summons after death and residing as bodiless spirits in Middle Earth. Though if all spirits must go to Mandos then ultimately all elven spirits would eventually be rehoused in bodies and reside in the West.
Ok here are the basics every intelligent being has a hröa (body) and a fëa (soul). In humans they are somewhat poorly matched. Only the Númenóreans ever really had them in close to being in synch. In men eventually the fëa will get weary of the hröa. In men when this happens they die and the fëa passes out of the world.
In Elves they are very well matched. But because the greater world is filled with corruption (originating from Morgoth), even elven fëa will eventually weary of their hröa. When this happens they eventually fade and become like wraiths, disembodied spirits. Being in Valinor is a much better place for elven fëa and the fading is almost completely halted. And a elven fëa that has lost a hröa whether through violence, accident, or fading can be reembodied if it goes to Valinor. But even after death, the decision to go to Valinor is still up to the individual elf. Even in Valinor though the fading eventually happens. The earth will have an eschaton though, where Eru will renew them in the end though.
So to answer your questions. As they fade the Avari increasingly feel the tug of the tug of the only place they can truly feel comfortable. And they would be allowed to go. Many will refuse and remain as powerless spirits, as you say to this day. Many others will only go in death. But even the Calaquendi can refuse to go the Halls of Mandos. So remaining a a disembodied fëa is always a choice. But I understand it is a rare one.
I don’t think it was a requirement that Namo re-embody anybody, at least not real fast. IIRC, Fëanor’s crimes were so great that it was expected he’d remain a fëa (ha, Fëanor’s fëa!) in the fastness of Mandos until perhaps after Dagor Dagorath, when he’d be let out to rebuild the rubble to create Arda Unmarred.
“The Sindar, by and large, became the Silvan Elves, and they’re part of recorded history, while very little is ever really recorded about the Avari.”
Some became orcs. It’s not hard to imagine Avari elves to survive and persist independently somewhere even after the departure of the three elven rings but all are sure to heed the call of Ulmo in time.
“At the end of the Third Age, most of the Calaquendi (the Elves who did go to Valinor) depart for the West by ship, with a few stragglers following later. What happened, though, to the Silvan Elves and the Avari? Did they finally opt to go West? Would they have been allowed aboard the ships? Or are they still lurking in shadowy forests to this day?”
Yes they leave. Legolas was one (presumably Sindarin.)
“Side question: When the Calaquendi are killed (in battle, say), their spirits go to the Halls of Mandos in Valinor, to rest, recharge, and get re-bodied. Nearly all of them then stay on in Valinor as opposed to returning to Middle-Earth. What happens to the Sindar or the Avari when they die, though? Do they wake up in Valinor, where they never wished to go?”
They fall under the doom of Mandos. They die and go to his halls, “…where long you will abide and yearn for your bodies and not gain mercy, even if the souls of all whom ye had slain should entreat for you…”
The only known Calaquendi to be set free from the halls was Finrod Felagund. Luthien was not under the Doom of Mandos but she gained Mandos’ pity and was freed.
JRRT changed his mind on that origin of the orcs. It’s mentioned in his Letters, I believe. And Christopher may have admitted he erred in including that in the Silmarillion, in one or another of his books.