Gabriel Witter: Dead or Alive? Beware of unmarked spoilers!Yes, no matter how many people want to give this angst ridden book the happy ending they believe it deserves, the question remains as to whether it actually did. There are many signs that point to the outcome that Gabriel Witter is alive, as well as Cullen supposedly reuniting with his brother in the end, but you can look past those signs and towards the symbols of something deeper.
The last page of the book implies that Cullen, after all the book titles he's listed in his journal, actually wrote the novel you've been reading, which wouldn't be the first time that's been done (having the main character write the book in question). Now, there's lots of unanswered questions at the end if Gabriel actually returned home alive. In fact, when Cabot Searcy's story connects with Cullen's, that's where the major Headscratchers start. But that could just be due to bad writing on Cullen's part. If I'm correct in saying so, Cullen mentioned earlier in the book that he'd never kill Gabriel in anything he wrote, and if Gabriel did end up dying in the actual story and Cullen wrote the events of the book like the last chapter implies, then Gabriel would not have died. He would have been saved from the start.
One who argues against Gabriel's death could say that if Gabriel did not die, then we would never have gotten the information about his kidnapping, but it is entirely possible that Cullen crafted the characters of Benton Sage, Cabot Searcy, and everyone involved, making them fictional in-universe. The part where Alma Ember connects the two is the hardest part to call fake, though you can go as far to say that Cullen crafted her, too, though that is even more unlikely. If Cabot wasn't crafted, and was actually a real person, it is still possible for the ending to be in-universe fiction as well. We're never given an explanation as to what happened to Cabot, and he beats Gabriel pretty badly before the end, possibly even beating him to death. If he was real, though, then there's no way Cullen could've gotten the information about what happened to Gabriel anyways. The farthest he could've gone was an educated guess after talking to Alma Ember, which he likely didn't do ever again after breaking her heart, and why should he go to her about her ex-husband anyways? He has no reason to. This is, of course, if Cullen actually wrote the book at all.
If Cabot wasn't crafted and the ending of the book was in order to keep Gabriel alive throughout the whole thing, then it's very possible that Cabot committed suicide by wrecking the car, killing Gabriel as well, if he hadn't already done that. The second-to-last chapter ends with Cabot realizing his destiny, which is never revealed, and is the last thing Cabot does in this story before he simply fades away, never to be mentioned again. If he did wreck the car, than it would've been found and the people inside were likely to be identified. This would actually give Cullen the information he needed to connect the stories without even knowing what actually happened when Gabriel was in Cabot's custody. It's safe to say that Alma would say something to Cullen if she found out his brother was found dead with her ex-husband, leaving Cullen to figure out what happened when he wasn't around, or at least take a guess.
As established in the book, Cullen likes to daydream. The last part where Gabriel returns is written in that weird format that begins with "When one is..." and goes on like that. Their reuniting is cut short by the end of the book, possibly because Cullen was short on details because it never happened, or possibly because he was too emotionally disturbed to go into detail. Either way a lot of it comes down to whether or not you think Cullen wrote the book. If you think he did, like the book implies, then the symbols behind the signs point towards Gabriel's downfall. If you don't think Cullen wrote the book, then it's possible Gabriel really did survive, thought there are still parts that could point towards his death. While it's mostly WMG, Cullen could've named the novel Where Things Come Back because he felt cheated that Gabriel did not, or maybe out of sheer irony due to the Lazarus woodpecker and Gabriel both being permanently gone.