She died as dawn broke, before Merlin even woke up.
Gaius tried to shield Merlin from the sight of his own dead mother on the floor. He couldn't, in the end. Merlin was to know the terrible mischief of the Old Religion one way or another.
Arthur might have woken, he might have returned to full health, he might have started kicking his knights about again. Merlin didn't know, lost as he lay where Hunith had long after he and Gaius and Gwen returned from the cremation ground, carrying her ashes in a silver urn—the best Gaius could afford with his pay.
Merlin's senses were all dead. Not even grief or guilt were allowed entry into his heart. He lay on the floor, then in his bed, for days on end, staring blankly at the ceiling and holding the hand of whoever it was dropping by every evening to sit with him, thinking about what he could have done, what he couldn't have done, whether it was even possible to bring someone back from the dead, whether Arthur was good enough... Whether the comparison was even justified—thinking about revenge and the dragon, shutting out the voices in his head.
But on the fourth day the hand-holder spoke, and Merlin was shocked from his numbness by Arthur's voice gently telling him, "I'm sorry."
Merlin turned slowly to see the prince staring at him, clutching Merlin's fingers tightly in his fist.
"My life was unworthy of being exchanged for hers," Arthur said, small and timid. "Gaius told me you tried to sacrifice yourself and were deceived."
Merlin rubbed his thumb slowly over Arthur's knuckles, surprised at the warmth and sparks rushing into his body from the point of contact. He swallowed the bile in his throat and looked back at Arthur.
"I know what it's like not to have a mother," Arthur ventured again, when Merlin didn't say a word but simply kept observing the blue of his eyes. "But I cannot imagine the agony of losing her the way you did."
Merlin dropped his gaze, then, unable to accept Arthur's sympathy. He wrenched his fingers out of Arthur's hand and pushed it away. The message was clear.
"No," Arthur said, getting to his feet. "You're my friend, you saved my life and suffered an incomprehensible loss for it. I owe you a debt for life, and I could never leave you to hurt alone."
Merlin watched with some confusion as Arthur bent to tug off his boots. Arthur straightened and placed a knee on the edge of the bed.
"Budge up," he said.
Merlin shuffled backwards, still mute. Arthur got on the bed and lay down beside Merlin with some difficulty; the bed was small and they were now both cramped for space, but right then Arthur gathered Merlin into his arms and rested Merlin's head on his neck, petting Merlin's hair carefully, and whispered, "I'm sorry.
"Hunith's life was worth a hundred of mine."
And Merlin didn't argue, not as he started trembling and heaving with sobs into Arthur's fancy clothes, grasping at the fabric and wishing dearly he were safe in his mother's arms instead.