Yeah, I think I would have been happy if it ended there. It's satisfying and there wasn't an overarching plot to begin with that needs wrapping up. The two main conflicts were trying to find opponents strong enough to take down his kids and whether he would ever acknowledge that they were in fact his kids and he was their dad, no matter how terrifying they were. And we got answers!
I think if this is continuing, an overarching plot may be necessary. Not because I want a super long, complex story, but as a narrative vehicle to explore more of this world and bring back recurring characters. Cause now that they've shown there are actually stronger people out there, we need a reason to see them. And unless he's gonna backtrack immediately next chapter, why would the boss intentionally send his kids into situations more dangerous than the missions he accepted in order to kill them? They won't settle for knowing they are "weak"