One of my alt's got them, then accidentally 'consumed' them and their experience into an artifact (IIRC). My assumption is/was they were just gone with no chance of getting them back (short of raising a support ticket or something, and since it was an alt didn't want to go through that hassle to do it). If there's a chance they're claimable again on a vendor, though, I'll have a look for that.
How? That shouldn't be possible and is definitely a bug. Only nth metal or another artifact can be fed into an artifact for XP.
That should not be possible. I just went into one of my toons that has the goggles and tried to feed it to an arti...it's not on the list of options. Delete? Yes, so maybe check your deleted items. Misplace...oh yeah for sure, check the bank. Salvage, yup...it happens, but as someone else pointed out, that would make it available for re-buy at the vendor (I think it's the 3000), whereas the others might not. Good luck finding them, but I'd really doubt you were able to feed them to an arti.