"The other gods win, the world's rather scoured and there are monsters running loose, they generously extend to Elves an invitation to come live in their paradise, some Elves accept."

Nod

"A while after that they pardon Melkor."

nod

...

"Wait what."

"That bit didn't make it out to wherever you're from? Yeah. They pardon Melkor, because it's been a really long time and he promises to be good now. And he pretends at it, for a while, secretly encourages a bunch of people in various forms of undermining the state, assassinates the King once the cracks start to show, put out the Trees, flees for this part of the world."

"Put out the... trees? You're going to have to explain that part it makes no sense to me unless my spell is going wonky, but I think it's fine... I think it would be a bit of a stretch to make this history consistent with mine, so I'm going to operate under the assumption that I'm on another plane or something, not just on the other side of the world from home."

"Another plane?"

"Yeah, like Hell or the Abyss or Elysium or...you don't have this concept, never mind. Another world, sort of. Some of them overlap each other, so that points in the one correspond to points in the other, the gods live in some of them, dead souls tend to migrate toward the planes with gods, but don't ask me how they get there I didn't really study planar theory much..."

"We go to Mandos when we die but he's in Valinor with the rest of the not-overtly-evil gods."

"Huh."

"Are there reliable means of interplanar travel -"

"Apart from dying? Yes, some of the more advanced spells transport someone from one plane to another. That's one of my main hypotheses for how I got here, I was in the middle of a battle with a wizard--well, rather a lot of wizards, actually--and then suddenly I was here. There are also supposedly magical artifacts for interplanar travel, but I've never seen one."

"Any way to scale it to evacuate this one entirely?"

"Um. Theoretically, maybe, but as far as your hopes go, no, probably not. Sorry. I'm not powerful enough, and I'm not sure I even know enough planar theory to even put the spell together and I've never actually designed a spell from scratch before. I know people who could, probably, given a couple decades but I am not one of them."

"Can you teach your magic?"

"Probably. And I can teach what I know of planar theory but it took centuries, maybe millennia, for people back home to develop the field enough to get the first plane shift spells working and even those can only carry a handful of people at a time.  Really, you should not stake your hopes on this. Teleportation might be more tractable, you could evacuate to Valinor?  That I could probably figure out in ten, twenty years. That might be an over- or under-estimate, every time I've learned a new spell before I've had books to help."

"Valar'd kill us. We might have centuries, probably don't have millenia. What else can your magic do -"

"Mine in particular, or magic like mine?  Magic like mine has very few limitations that I can think of, for the best practitioners. Though usually their abilities are confined by their area of study. Control the weather, heal the sick or wounded. Raise the dead, though very very few people can manage that without petitioning for divine intervention. I've heard of people creating or moving islands, or making private planes. Moving continents should be possible but I don't think there's ever been anyone powerful enough. My talents in particular--"Best not tell him everything, don't know how trustworthy he actually is--"You've seen me throw fire and acid, I can do a couple more like that, and can vary the dispersal.  Invisibility, you've seen. I can sense other magic, but it takes time and focus.  I can change my shape, with limitations. Languages, obviously, though that also takes some time."

"And all of this took millenia to work out how to do in the first place -"

"A lot of it was quicker to develop than that.  But planar travel, resurrection, summoning spells--they all needed a lot of background about the nature of the planes, and that took a while to develop. In theory, that research is faster now, but only because we--they--have those tools. Easier to figure out what Heaven's like when you can visit, or call up an angel to answer some questions."

"We don't necessarily need those right away, just something that could kill a god."

Malak narrows their eyes "Oh, I see. Unfortunately I don't know anything about killing gods beyond 'it's really really hard.'"

"We've noticed. Anyway, we pursue Melkor across the ocean and manage to kill the armies of orcs and besiege him in his fortress for four and a half centuries, and then the mountains around the fortress all erupt and kill everyone within a hundred miles and that was the Battle of Sudden Flame and that's a very brief history of the war."

"And then Nargothrond's king ran off to get himself killed. Did he lose loved ones to the fire, or did the Enemy capture them, or he just...ran off. Did anyone actually see him run off or did he just go missing?"

"Both his brothers had kingdoms in the north that fell with no survivors, and while he was riding up north in what would prove a futile mission to rescue them, his escort was ambushed and took serious losses and was rescued by some humans. He gave the leader of the humans a ring, swore him friendship in any need, arrived north too late, came back - he was torn up about it, of course, but functional.

And then the human's son showed up. The human had died, and the son had gotten it into his head to marry Lúthien, and her father had told him that the bride-price would be a Silmaril off Morgoth's crown. The Silmarils being extremely powerful extremely dangerous magic objects that my grandfather died trying to keep from the Enemy - my father made them - you don't need to know what all they do beyond that if we had them we'd have won the war long ago - 

- anyway, the kid takes this as 'so I have a chance' and shows up in Nargothrond to ask the King to help him steal a Silmaril off Morgoth's head, and the King agreed, and started mobilizing the kingdom for a suicide mission to try it."