User blog comment:TheManOfIron/Andrew Ryan killed himself./@comment-97.75.121.81-20130820194251

Ryan knew the city was doomed, in the sense he wasn't going to be able to fight Atlas/Fontaine anymore. Even if he could "turn" Jack, my impression was the EMP bomb at the end really blew a lot of the defenses that was keeping Ryan safe and somewhat in control.

Therefore, he resolved to destroy the city and have Jack kill him. "A man decideds, a slave obeys". Before the city blew, Ryan's last act was to be a man in control by deciding to die, and in the end show Jack that he was just a slave obeying commands.