Friendship is also a big theme. Just like in the original works, fanfics might show characters from Naruto and HxH forming strong bonds. They could be teaming up against a common enemy or just learning from each other's ways.
Another one is 'HxH in the Ninja World'. It follows the story of an HxH character who somehow ends up in the Naruto world and has to adapt to the ninja way while still using their HxH skills.
I don't think so. There haven't been any official announcements or indications that the HxH manga will continue. But you never know, maybe there'll be a surprise in the future.