Disclaimer: I do not own any of the Buffy the Vampire Slayer or Angel characters or plotlines. I do own Julie, but all the other characters belong to the BTVS and Angel franchise.
Sunnydale was not destroyed at the end of Chosen. The school was, though. Spike did have to give his life in order to save the world, but came back to Sunnydale and Buffy after spending a short period of time at Wolfram and Hart with Angel. The potential Slayers were never activated. Tara didn't die; Oz did in her place. Anya didn't die either, and Xander didn't lose his eye. The Watcher's Council was replaced with a better one that Giles is the head of. I think it is safe to say that this story doesn't really follow Chosen much. Wolfram and Hart was disbanded, and moved the gang back to the Hyperion, but still sometimes refers to his business as Wolfram and Hart. This story doesn't really follow the Angel plotline.
Plot: Spike and Buffy go out one night to patrol. They meet a very mysterious girl with strange powers, who claims to need the Scooby Gang's help. She has a ring that if it falls into the wrong hands will bring the Devil to this plain of existence. The Scooby Gang agree to help, and along the way have their lives quickly thrown for a loop, and turned upside down.