Carl came in guns blazing on The Walking Dead in "Sing Me a Song," but it wasn't enough to take out Negan – it was just enough to get his attention. After sneaking into the Saviors' compound, the Sanctuary, Carl was ready for a fight. He killed two Saviors and for a moment it looked like he might have a chance to shoot Negan. Carl missed that chance and instead earned himself a guided tour through Negan's home, complete with snack trays and mind games. Throughout the episode Negan promised to punish Carl for killing two of his people, but he never made it clear just how that punishment would roll out. So does Negan kill Carl on The Walking Dead?
Negan took his sweet time when it came to dealing with Carl: he showed him around, asked his questions, made fun of his eye, and forced him to sing. But he didn't physically hurt Carl, even if he did threaten to by waving Lucille fairly close to Carl's face. Eventually Carl got over his fear enough to ask flat-out what Negan was planning, which was when Negan explained that torturing Carl and breaking his spirit was both more effective and more "fun" than killing him. That Negan has some interesting hobbies.
But Carl wasn't cowed. The only time he showed even a modicum of fear was earlier in the episode when Negan demanded Carl remove the bandages on his eye, which brought Carl to tears. Watching Negan torture one of his own men shortly after that seemed to strengthen Carl's resolve instead of weakening it. Carl had suffered through the full Negan experience and lived to tell the tale, and he came out of the experience more angry than afraid.
Carl's lack of fear was what Negan respected about him. In the few moments that Carl's tough facade did crack, like when he cried, Negan didn't really seem to enjoy it. Instead he apologized to Carl and almost appeared remorseful – as remorseful as Negan gets, anyway. Negan was definitely intrigued by Carl, particularly because Carl could stand up to him. Much like Daryl, it almost seemed like Negan could see how Carl could potentially be useful to him. And Carl would definitely be more useful alive than dead.
At the end of the episode, Negan returned Carl to his home in Alexandria, safe and sound. That may not last forever, but Carl's bravado definitely bought him some time.