All Age of Apocalypse appearances in chronological order :
Tales of the Age of Apocalypse #2
X-Man #minus 1
Factor X #1-4
Dark Beast seemingly died in Uncanny X-Men (3rd series) #22 as the end result of his ongoing self-experimentation. He returned without explanation in Secret Warriors (2nd series) #3. It was later revealed in Uncanny X-Men (5th series) #13 that Mister Sinister saved his head and regenerated it onto a new body.