I also found a bug after I killed the bird on the low-friendship route; not only does Huy NOT join the party after I got out, but the "hidden route" that was only supposed to be accessible on the high friendship route is open, alongside the low-friendship one. Going up there also breaks the game, as Huy is NOT visible, and won't pick up the star half.
Edit: It'll also prevent the button across the waterfall from ever being pressed, as Huy won't jump across (cuz, you know... he ain't in the party).