Maybe Samedi simply didn't die

My theory on Baron Samedi appearing at the end is that the man on the train is he himself. He simply faked his death and still lived at the end of the film.

He seemed a wily customer throughout the film, and never showed any particular loyalty to Kananga compared to, say, Tee Hee. Whilst not calling him a coward, he would have known that if it came down to a fight between Bond and himself, he would lose easily and be killed. Really, he was all style with little substance. He hoped that the crowd would kill Bond for him or his showy tactics with the fake Baron etc would scare Bond off, but when that failed he simply 'fell' into the coffin which was left with snakes that had the venom/fangs removed.

The man chose the same snake from the start of the film to kill the girl, which seemed odd given the huge number of snakes in the coffin. So it isn't entirely silly to suggest the other snakes in the coffin were harmless and just for show.