Kageyama stays with Karasuno in the manga. His character development and contributions to the team continue without him leaving. The bond he forms with his teammates keeps him committed to the club.
Sure, Karasuno beats Shiratorizawa in the manga. The match is full of thrilling moments and showcases the growth and determination of the Karasuno team.
Captain America would probably be very reflective. He might see his past self as a reminder of his long journey and how much he has changed. He could try to offer some words of wisdom to his younger self.
Some gods might be entertained. For instance, Hermes, being the trickster god, might enjoy seeing the different and often humorous takes on the gods in the fanfiction.
In the manga, Hinata doesn't outright beat Kageyama. Their relationship is more about mutual growth and competition rather than one consistently defeating the other. Both characters have their strengths and weaknesses, and the story focuses on their development together on the volleyball court.