Question: What has ended up with Max? Billy promised to go back and release him, but we never see that happen, and no explanation is given for that in the Epilogue. Is Max a real figure? If he is, what has happened to him? Did he manage to escape, or did he die in prison?
Answer: It's never stated what happened to Max. The film was a heavily fictionalized version of Billy Hayes' book, and the Max character appears to be fictional as well or at least a composite of other real-life imprisoned Westerners that Hayes met while in a Turkish prison.
Answer: Max WAS a real character, and a Dutchman in real life, rather than an English one as portrayed in the movie. He eventually got paroled and later treatment for a severe drug addiction he had too.