Fëanor's sons are carrying him, but he can scarcely feel their hands anymore. The flames of the Valaraukar ("balrogs," he reminds himself, in the Sindarin) are still licking at him - not just in body, but in spirit as well. Too many of them. Too strong.
"Stop," he says, holding up his hand.
They stop.
He tries to gather his thoughts, but he can't help staring off at the peaks of Thangorodrim. (The nearer mountains, he reminds himself, are named "Ered Wethrin" in the Sindarin.) Even the whole host of the Noldor, he is now sure, cannot overthrow them. The whole Host of the Valar could scarce overcome Utumno; what can he and his people do?
The fire of the now-futile Oath rises in him. No, he can't say that to his sons. He can't tell them aloud that it's futile.
Instead, he opens his mouth and curses Morgoth again, three times over. "And," he says - feeling the fire in him - "the oath you have sworn by Illúvatar, be sure to keep. And in keeping it, avenge my death."
Then he releases his grip on his body, and the last thing he feels is the fire consuming it.
(And then - as he should have known - he feels the taint of Morgoth grabbing at his spirit, and a passionless summons for it which he knows is the Valar. He throws all his passion and curses against the grabbing of Morgoth, knowing that will leave no energy to resist the summons of Mandos.)