While some Scooby Gang characters like Giles received happy endings at the conclusion of Buffy the Vampire Slayer, canonical comic book continuations reveal a grisly fate for the Watcher. After the show ended with Season 7, several more "seasons" were produced in the form of official canon comics from Dark Horse Comics and creator Joss Whedon. While BOOM! Studios is currently continuing the legacy of Buffy through its Slayerverse, the Slayerverse compiles stories from different universes of Buffy. Audiences follow the same characters with origins and mythos slightly tweaked from how they are presented in the TV show.
Although these multiverse stories aren't necessarily non-canon as they don't disrupt the main universe, they don't follow the same narrative precisely as the TV show. The comics crafted by Joss Whedon and Dark Horse Comics, however, are considered official canon to the main Buffyverse given that Whedon and FOX approved all stories at the time of publication. These canonical comic seasons allowed audiences to receive full closure for characters who may not have gotten such closure in the finale.
Take, for instance, the Giles character. In the Season 7 finale, Giles is seen taking part in the final battle and being one of its survivors. There isn't any major indication for what will come next for Giles during the episode, but his character continues to develop as one of the heads of a global Slayer organization in the comics. A secret alliance with Faith to kill a Slayer destined to bring about the Apocalypse leads to them exiting the organization. It isn't until the introduction of a new Big Bad, Twilight, that Buffy and Giles reunite. It is through this encounter, most notably seen in Buffy the Vampire Slayer Season Eight #39 (also titled "Last Gleaming, Part Four") by Joss Whedon and Scott Allie, where Giles is killed by Angel.
How Does Giles Return From The Dead?
The issue in question sees Angel, possessed by the aforementioned Twilight, snapping Giles' neck similarly to how he snaps Jenny Calendar's neck when he was Angelus in Season 2. When Angel finally recovers consciousness, he is wracked with guilt. Even knowing he wasn't in the right frame of mind, he still feels responsible for Giles' death. In his mind, the only way to free himself of this guilt is to bring the Watcher back from the dead.
Through a complex ritual, Angel is able to compile lost fragments of Giles' soul and return them to his corpse. The ritual itself is successful, albeit with side effects. Specifically, Giles returns to the living not as an adult, but as a child forced to relive his entire life all over again. This wouldn't be a total loss, though, as before the comic continuation of Buffy the Vampire Slayer concludes, Giles is able to rekindle a romance with Olivia Williams (seen in Season 4 of Buffy) and is appointed the vice president of a reformed Magic Council, working under President Buffy Summers. While Giles is able to eventually find closure, he first had to endure a brutal death at the hands of one of Buffy the Vampire Slayer's heroes.