Of course Link can't accept that. It isn't (just) that Nero is invoking some strange sense of sympathy for the actual embodiment of the apocalypse in him. Nor does Link object to putting Ganon out of his pathetic and sad misery, in some fashion or another.

He just can't accept that he's left Zelda to fight alone. Again.

"I'll find a way," Link says, with the kind of stony-faced determination that suggests he won't be swayed otherwise. If dying didn't stop him, why should this?