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.
"I think it worked, but I can't actually tell the difference between an enforced order I'm following or have no opportunity to disobey and an unenforced one under the same conditions."
"Do not give anyone orders. Do not give any other fairies names so they can give orders; Tell me if there are other fairies trying to do that, and stop them if they do it to me." Intent might not be audible but he says it rather forcefully anyway. "Yesterday we were trying to make progress on the questions of which variants on a general demand for information I could make without harming you."
"I don't mind telling you how fairies work. It's - stuff about me personally that I don't want to talk about as much. I don't know if you're going to be trying to use me as a strategist or just a fairy, that makes a difference."
"You'd have five hundred years of situational information to catch up on to be useful as a strategist. If you find it more objectionable to be asked to think about problems for me I can -" he flinches - "just use you as a fairy. You do not have to tell me anything personal. If you want to ask compensation for telling me things or doing things for me, I can do that."
"Being under orders to think about a thing is - unpleasant. Being asked to think about a thing isn't. I don't know what I'd ask for. You don't have my tree. You don't have a gate. You're letting me have books and paper and everything."
"I'm not accustomed to having good company. I don't know if I like it particularly. Music's all right. I don't know what mortal foods taste least weird yet."
"If you're going to use me on something horrible anyway I would rather have warning and a chance to think of less horrible ways to do it."
"The thing I am sworn to retrieve is held by a young mortal woman who is the ruler of a settlement to the south of here. It's not even really a settlement, more of a refugee camp, filled with the survivors of the collapse of the last kingdoms on this continent. And their children. The Enemy hasn't attacked it yet, perhaps because it's not worth his time, perhaps because he expects me to do it. I have asked her to give back the thing I am sworn to retrieve. She has told me to come and get it. We have an army. We are going to do that."
"Before she held it, her father did. We made the same request of him, for the same reason, and he refused. He thought that its blessings would protect his kingdom from the Enemy. They might have done so, for a little while. We attacked her father's kingdom. Her father, her mother, and her brothers, who were young children, were killed in the fighting. As were many tens of thousands of other innocent people. So now she hates us and is eager for us to ride to war so she can avenge them."
"I don't really have a good grasp on the significance of children as mortals - or whatever you are, but it keeps sounding like you can die - have them. Or even as breeder fairies have them, but I assume that's different."
"Killing children is considered very wrong because they are very small, and defenseless, and cannot hold weapons or harm anyone. In this world 'mortal' is used to mean people who will die after a certain span of years - we are immortal in that we will never age and can live all the lifetime of the world, but if you drive a sword through us in the right place our body still can be damaged beyond the capacity to sustain us. Does that not happen for you?"
"I'd heal eventually if there was a big enough piece. I don't know exactly what would happen if there wasn't but I wouldn't die."