I don't think Bada is "removed" as seongchan's cousin. In the end, we see Doha saying "you're Pi seongchan's cousin right? Pi Bada." Implying that seongchan was "lost" and only Bada was found. Otherwise, if Seongchan did survive, them Bada would be the one lost instead. And the fact that the author did some character notes at one point noting their college majors, it implies that they did exist already before getting into the game in the first place. But this is just my take on it, it's how I understood the ending and combined with the author's notes that imply their existence in the real world.
But that would mean Bada was never an NPC?
On a side note, I just realized that the author putting the characters' college majors and including one for Bada was def major foreshadowing I didn't catch (*_*)
I mean, I'd like to think they are real people who got stuck in the game, and because pi seongchan left his bag, and asked his cousin Bada to get it, Bada became an NPC who was also stuck in the loop. If Seongchan hadn't left his bag, then Bada won't be an NPC and the one who "warns" them might be another person. This is just my take on the story though, I just assume that the fact that they had irl majors it would imply that before they were players and NPCs, they were just regular humans living in the real world without the loop.
Sorry if I'm being too technical but the ending makes me wonder—if Bada is an NPC who's now become a real person, does that mean real world Seongchan never had a cousin in the first place but now he suddenly does? If that's so, does that mean Bada suddenly has people in the real world who know him? I wonder how the side stories will play out, if we get any >.<