I think the Writing forum is a good place for this question, so I moved the question to that forum. I don't know if this will be interesting to you, but I wrote an article about writing for games. I'm not sure if you're interested in “the process” of writing game dialogue, or “the format.” When you say “written out like a screen play,” it sounds like you're asking about the format. I imagine the regulars in the Writing forum will agree with me that the format of video game story dialogue doesn't have to follow screenplay format conventions.