Exactly. It's as inconcievable as, for example, a hobbit and his servant simply walking in to Mordor. Can't be done, so no sense taking precautions to prevent it. History is a flat circle...Look, one elf sneaking around the huge Thangorodrim range isn’t worth considering a risk of any kind. Even if he by some weird chance would happen to stumble upon the one Morgoth nailed to the cliff, he would have to cut off that one’s arm to free him. And then what? His little redhead chum would die soon enough, and none of them would come back to their fine friends, all alone as they are.