Finarfin could not promise to kill Maglor. And at that moment, France was very close to that ancient part of himself. Close enough he could not make such an Oath even if he wanted to.

That light, of Valinor, of the Trees, was lost to the nation. He was still old. Still powerful. But that brilliant light was gone. Seeing it in Maglor's eyes thouh brought back the ache of what had been, for all that he tried to tamp down on it.

But the rest of what he saw in the elf's eyes bothered him, for all that he understood the outlines of the cause.

Instead, after the acceptance of his words, France nodded slightly, once, and nudged Maglor up. "Come. Let's get you cleaned up."