Yeah, it's the best choice regardless of what happens. Well, almost. Being his friend could put them in trouble with the next demon king if it's not him. But in that case you'd likely have a demon king you'd want to subjugate anyway.If he does become the demon king, it's a really good investment to become his friends now when he's still not the king. If he doesn't, they were still able to explore the demon royalty exclusive dungeon, which is also excellent for an adverturer.
i mean he is barely a teenager, so it's understandablebitching all this time that he doesn't want to be the demon lord, now that someone else might take his place he becomes desperate.