What sad terrible news. I finished reading the Silmarillion just last week, and was impressed by how he turned loosely associated stories and myths into a single, cohesive narrative that even had full continuity with LoTR. Just this week again I was marveling that he was still around.
I don't see a person dying after 95 years of a well-lived productive life as terrible. That's a pretty pathological view.
Celebrate his life. And maybe read some other things about the many much more healthy perspectives cultures around the world have developed around death.
Sadness is fine, that's part of processing a loss. But neither this loss nor the appropriate sadness are terrible things.
If you read Tolkien (John, not Christopher) death is a gift given to Men that even the Valar (essentially the pantheon of Arda) do not understand. It is certainly not viewed as a negative.
It doesn't carry much weight when we write how lucky we are to be mortal, since being immortal has never been a realistic option.
It brings to mind how Iain M. Banks wrote in the Culture series about beings who chose functional immortality by uploading their consciousness to networked hardware. One of them still programmed himself to need to pee in the simulation, because he liked doing it.
Whereas I'd be surprised if any being programmed themselves to die in the simulation and be wiped away.
But if they did, I'd love to know their reasoning.
In the Culture, for biological beings, it is considered in bad taste to live more than a 4-5 centuries. Although effective biological immortality is possible, at that age most Culture citizen choose to die, while a some upload themselves or become drones.
I do not remember the books go too much into details about the reason for this tradition though.
The Valar and Maiar are explicitly not a pantheon, just as the House of Stewards are explicitly not kings. The Gift of Men is terribly obvious in that light: they get to strut and fret their hour upon the stage, then go directly to join Ea Illúvatar. The Valar cannot hold them, they go to join the heavenly chorus. The message is not as direct as in his friend C.S. Lewis’ tales, but it’s there.
If you prefer to term Eru, together with the Ainur, a pantheon that would be more appropriate. The Valar are more like the Olympians as the subset of this pantheon most relevant to Arda.
Also, I don't believe it's said that Men join Eru in death. Just that they will take part in the music after Dagor Dagorath. I think you're sweeping numerous other mythological influences under the rug if you choose to view that as predominantly Abrahamic in origin.
He definitely suffered some personal tragedies - there were allegations of sexual abuse at the hands of some passing Oxford acquaintances of his father IIRC
