No Living Man

[Nilpaurion Felagund]

Only Éowyn (with the help of Merry, of course) could have killed the Witch-King. No other.

To prophesy you have to go beyond the constraints of time and see . . . well . . . time. Case in point: Remember the vision of Ainulindalë? This is where the Ainur got some of their prophetic ability from. Add to that their personal contributions to the making of Eä, they know pretty much more about the future than anyone else in Arda.

So, when Glorfindel says, "Far off yet is his doom, and not by the hand of man will he fall," he already saw Witch-King's fall in Minas Tirith, brought about by Éowyn. As Éowyn didn't exist yet at that time (or perhaps the vision was not clear--I don't know), I don't think he could have put a name to the face he saw.

Of course, this introduces the predestination vs. free will debate into the mix.