Augh, Nonnie. SO SO TRICKY.
*stares a little worriedly at the ask*
Okay, let’s try something. We know that Orcs are descended from Elves that were corrupted by Melkor. So, perhaps it is that they go to a separate part of Mandos’ halls.
We also know that Mandos holds onto those souls that need to be held *smiles sweetly at Feanor*. He keeps them within his halls and does not allow them to be reborn. It’s like Elven purgatory, I suppose.
So Mandos probably doesn’t allow those souls to be reborn as Elves until they have been renewed, refreshed and uncorrupted? idk. That’d take millennia for some of those Orcs (hey hey Azog, cheers Gothmog, you boys are nasty).
Considering that the entire recorded history of Middle-Earth isn’t actually all that long, I suggest that many of those former Orcs will only be released after the final battle, when all evil and sorrow is finally gone from the world and everybody can start again.
Okay – that’s ONE idea! I’m sure other people have other ideas, though. I hope it’s helpful to you, Nonnie! 🙂