Tolkien becomes an agnostic

[Evan]

That being said, one "least impossible" time might be after Vatican II. The infallible teaching Magisterium of the Church was now saying new and things nothing like what it'd said before. Were they changing doctrine? Or simply reexpressing it with new emphases to minister to the new age? Thousands of Catholics concluded that the Pope and bishops had fallen into heresy. Tolkien himself refused to accept the English Mass, loudly saying the old Latin responses over everyone else's English.

So... still hugely improbable. But probably less impossible than any other post-LOTR time.

 

[overoceans]

The man went to mass every DAY.

So did Dr. John Rock, but I believe he still fell away from the Church, and religion in general, after numerous battles with Rome over his famous pharmacological gizmo.

 

[jahenders]

Well lets us suppose that the change in his beliefs occurs AFTER the printing of the LOTR trilogy.

With that out if the way, I think Tolkien will revise his backstory of the Elves and the Eldar. He might also go to the time and trouble to revise the books when they may be reprinted. If so, this could really cause conflict with his fans and readers down the road.

He was constantly revising the Silmarillion before, and after, the publication of LOTR. So, if he (somehow) became and atheist AFTER writing LOTR, he might make some modifications to it and other stories. However, he was pretty devoted to logical consistency, so I can't see him either changing LOTR after being published, nor changing the Silmarillion to such a degree that it clashed with the mythology in LOTR.

If he became an atheist while still writing LOTR, he might potentially decide to make substantial changes. However, if he pursued this, it would take him quite a bit of time and he might miss the window of opportunity where the publisher (and public) were interested in a 'sequel' to the Hobbit. If he makes dramatic changes the end work could potentially also be less appealing to readers and might never gain the fame it has.

 

[Zurirach Adankar]

Since the motive of a great fall appeared in several important parts of his mythology (fall of melkor, of the Eldar, of Numenor) , and the concept of this great fall seems much religious to me, his mythology may change in many ways.
But it is nearly to late for him to change his mythology after he finished the Lord of the Rings or if he is at the End of writing the Lord of the Rings. If he is in the middle of writing the Lord of the Rings he need to rework his hole mythology which could take at least several years before he could go back to the Lord of the Rings.

He would perhaps "kill" Illuvater out of his mythology, maybe the Ainur are still there, but they perhaps don't have as much knowledge about the cosmos as before.
Changing his worldview could change his perspectives entirely. Perhaps he could abandon his concepts of Good and Evil. This could lead to more Eldar like Feanor and his Sons, or more conflicts between different fractions of the Eldar.
I wonder what will happen to Melkor. Tolkien still needs great conflicts for his stories. Perhaps Melkor remains but thinks that he himself isn't evil but does great harm.
I think Tolkien wouldn't abandon the core stories of Beren/Luthien, Turin and Gondolin.