It takes as long as the spring only because they weren't looking. They can stretch the oath that far, they can be disinterested in knowing - but now they know, and so there it is. Elwing of Sirion is twenty-three. Half-man, so fully grown. Sirion is a city of refugees. Elves and Men and, since there are Men, children. Elwing herself has infant children.
They debate whether to send messengers. Debating is allowed, even protracted debating. The Oath, these days, is loud in their minds, and louder when they're pushing it like this, but they drag out the debate for a few months. Messengers will probably be shot on sight. The last time Elwing of Sirion received news of the House of Fëanor it would have been the news that her brothers, twins, aged seven, had not survived the sack of Menegroth.
They send messengers anyway. The messengers are shot on sight. They have good armor, Fëanorian armor, and return home injured but not lethally. Maglor's songs no longer stitch them together. War makes you worse at healing. Maglor's songs are more powerful than ever - he can knock back a wave of approaching enemies, he can make a blade's next touch deadly, he can make them faster and more impervious to danger, but he can no longer do healing.
Maedhros, when he thinks about this, thinks that perhaps there needs to be part of you that is not broken for healing spells to draw on. Or perhaps the Enemy is amused to strip that away first. Perhaps the Enemy finds it suited to the theme as the Oath tugs and yanks and twists them into violence against the lands they once defended and the peoples they once sheltered.
They send messengers to Sirion again. The messengers deliver a plea for the Silmaril, an offer of anything at all in exchange. The messengers do not return at all.
The Enemy is many many hundreds of miles from here but at night Maedhros can hear him in his head. Is it so implausible that I really let you go? the Enemy likes saying. You serve me better free than you ever would have willingly.
The Oath allows them to work slowly. They begin planning the sack of the refugee camp even more slowly than the Oath allows, so slowly that its currents are constantly tugging at them. Any slower and the currents would erode all the things they care about which are not the Oath, and it would be a disaster to go to Sirion once they've been stripped of their capacity to care about anything that is not the Silmaril. So they do not hold out forever. But they work as slowly as they can.
"When I have sorcery I can make plants grow very fast. ...Which I guess also doesn't make sense with the essences thing."
"In our world the formal definition of magic is things which create essences, allow essences to undergo unfavorable transformations that they usually wouldn't, or create energy. I had a brother who thought that it was inelegant for magic to be three different things like that, and concluded that all three of them are actually somehow the same thing."
"Fairyland has a lot of things that behave in ways that sound like by that definition they'd be magic even though no one ensorceled them. Sourceless waterfalls and stuff."
If you were like us and ate nothing but leaves you'd have a hard time building any muscle. We mostly eat animals and animal products to get protein.
Come to think of it, you weigh far too little to be made out of the essences we are. I wonder if you're just made of something entirely different."
"No insects either. Lots of flowers! Plants mostly pollinate themselves, although some kinds of fairies pollinate them to help them along."
"Maybe. They didn't tell anybody they did it, though. And there's the regular mortal world, too."
"I've never been. And I only met a mortal for a little while like - fifty years ago, about. It's full of mortals, they come in different colors but only one kind really, and sorcery doesn't work there either, and they have weird politics and lots of languages and no magic and lots of animals but I don't think they have Valar."
"They live in cities, really dense cities, the mortal - she kept going through nicknames, I can't remember which one she had last - was talking about buildings a hundred stories tall, and they can't fly so they had things that could roll very fast along the ground with mortals sitting in them..."
"Yeah, I don't think this is the same place or I'd be more optimistic about finding a gate in the next couple thousand years."
"How would they possibly do that? Nobody even knows why sorcery doesn't work outside Fairyland."
"Preserving the divine light of Valinor so we could live outside it. Making it possible to talk instantly with anyone anywhere in the world. Armor like mine, which -" he smiles bitterly - "is enchanted so thoroughly I am almost impossible to harm in battle. Besieging a god for four hundred fifty years. Inventing new chemistry and biology along the way so we could figure out why Men died so easily, inventing music and fortresses that let us stand against a hundred times our numbers..."