I get the feeling Ammano's character might stick around longer than six episodes if he's popular enough. After all, Bishop was only meant for a six episode arc and he pretty much becomes the big bad of the series.
And yeah, I think Scorpio's going to return at some point, or at least we're gonna have Sonoda stick around for a while. They've never killed off a main character that shows up at a press conference. (sans Otoya)