You don't have to tell them. Clearly you're capable of not doing it. But if there's some way around it - maybe not the memory thing in particular but that still seems really promising to me honestly -
Why couldn't you - tell some witnesses that I'm going to make you forget a thing, your informed opinion is that you don't want to know it except on some occasional basis, and - then you'll be better and you can go home and on an occasional basis I can let you remember it for a short time and you'll be nearer Fëanáro at those times than you usually are now -?
And then everybody knows that when you have the memory you don't want it, and that constitutes your informed consent, and then I guess everybody runs interference so you don't pester me at all hours of the day but it seems better than you wasting away here. There might be a better idea, especially if I can think of a loophole you couldn't - if you were willing to tell anybody, I mean, the Valar would just reembody him right away and you'd be done, but I understand why you can't bring yourself to do that -
If you were willing to tell people, I imagine someone who has been here for a while and doesn't need to be alive right now in particular might be willing to test it out. And - and I don't know about Eldar but on my plane people recover from the most horrifying sorts of things happening to them in their childhoods up to and including being murdered by a parent and then resurrected, it's not common but it's happened, it's not easy but it's doable, and you I don't know what you're going to do if the memory thing doesn't work and it's as airtight as you think it is - is there no way to release an oath -?
Then in the long run how is even being dead going to help, you have to do something else...
I'm honestly not trying to therapize you for anyone else's sake but your own, but you do keep bringing up what would happen to Fëanáro if you temporarily killed him and I'm not sure why you think that would definitely be worse than what would happen if you died.
He thinks it's his fault. And - and I haven't known him very long but my read is that - that he'd cope better with thinking it's his fault but he fixed it, than with thinking it's his fault and it's never, ever going to get better.
Well would be an exaggeration. If I thought I could convince him it wasn't his fault that might be a different matter, too, but I tried telling him and it didn't work.
And if we could come up with a way for the forgetting thing to work you wouldn't even have to do that.
...okay, you'll tell people your informed preference is to forget the thing?