Slowly, Hermione joined him on her knees in the middle of his tiny dark room. For a moment, she didn't say anything. She didn't have to. She could have argued that they all missed him, that they wanted to see him around the castle again, and that he didn't truly want to be left alone, but none of it would sink in quite as much as if she let him realise it himself.
"Neville?" she eventually said, quietly, when his sobs had died down somewhat. "We're not leaving you. Magic or no magic, you're still Neville, and you're still our friend. You matter to us. Muggles... Muggles are perfectly happy living without magic. It'll be an adjustment, sure, but it's still just as rich a life. You'll be happy! And you'll still have us."