I\'m dealing with game dialogue files (conversation between player and non-playable-characters) where dialogue choices and their outcome depend on certain conditions and res
Because you're writing this in Ruby I think that doing it in XML should be sufficient. That way you could make a web application that allows you to work on the dialogue and game logic from anywhere. And other people can collaborate with you, or possibly create user mods - which is always a plus.
As long as you keep your XML files well organized (flowcharts on paper will help) you shouldn't run into any issues, and might even thank yourself for going through the pain of parsing it :)