Morgoth technically is able to witness what occurred in
Middle-earth from the Void.
Remember that Morgoth's essence and "will" are effused throughout Middle-earth, and that this is a central feature of his Rebellion during the
Ainulindalë.
Tolkien points this out in one of his Essays( The
Wikipedia Article on Morgoth's Ring contains this quote, but not the source - I will track down the source to eventually correct this on the Wikipedia pages):
"Just as
Sauron concentrated his power in the
One Ring,
Morgoth dispersed his power into the very matter of
Arda, thus 'the whole of
Middle-earth was Morgoth's Ring'."
Like
Sauron's
Ruling Ring, this did not allow Sauron to perceive directly the Ruling Ring itself, yet there is a marked difference between Sauron's Ruling Ring, and
Morgoth's Ring (Ëa,
Arda, and Middle-earth).
Everything within Ëa contained a part of Morgoth, whereas only Sauron's Ruling Ring (and to a lesser degree the Seven and Nine) contained a part of Sauron. Sauron could "Sense" to a degree the Ruling Ring, which helped him to know it when he laid his eyes upon it, or when one of his Servants was near it, and the Ruling Ring worn.
Both Morgoth being in the Void could see all of Ëa, and perceive slightly that part of himself still within Ëa, dispersed as it were.
And Morgoth's reaction to
the Third Age would have been the same reaction he had to
everything: Hatred.
Morgoth hated his own existence most of all.
In Christian Theology, this would be due to his willful separation from
Eru/
God. And this would be made all the more painful for Morgoth, because unlike Humanity, or the
Elves, who had never seen God (Eru - but the Elves and
Edain HAD at least seen the
Valar, who were the direct product of the Mind of
Eru Ilúvatar/God) and thus had to rely only upon Faith (of a sort - because, as I mentioned, at least the Eldar and Edain
had SEEN the Valar, and thus knew that they were not being lied to regarding the existence of Eru Ilúvatar). This absolute knowledge would have been extraordinarily painful to
Melkor Morgoth. And due to his Pride he refused to take responsibility for his rebellion, and thus blamed Eru Ilúvatar for his pain, hating him all the more for it.
He would have raged and cursed Sauron for Sauron's blindness and arrogance in losing to the
Númenóreans, and underestimating the capabilities of Humanity.
He would have raged at the salvation of
the Faithful at the Drowning of Nú
menóre, and raged all the more at Sauron for having failed in something that should have been so simple.
He would have raged at the Last Alliance of Elves and Men.
He would have raged at Sauron's loss of the Ruling Ring (and delighted in
Isildur's betrayal of what is
Good in keeping it.
And most of all he would have raged at all of his creations allowing their consuming Pride and Arrogance from keeping them from working together to rescue him from the Void.
He would most especially have hated
Aragorn Elessar Telcontar, who was the rebirth of
Westernesse and the lineage of every one of Morgoth's greatest enemies of the
First Age (
Ainur,
Elf, and Man - from all three was Aragorn descended).
But this rage and hatred would have been impotent, and Morgoth would have raged and hated himself most of all for this: That he was impotent to do anything, save for waiting for the
Evil with which he had infected Arda and Middle-earth to spread more corruption and discord before it finally failed at last before the
Dagor Dagorath.
MB