Humans are adaptable and really good at ignoring problems if those problems seem to be 'solved'. There's a funny little comic called the Door In The Kitchen, that deals with that in what I feel is a realistic way.
But they could have handled it better. Maybe have a few characters who aren't from the city, and talk about how much more dangerous things are out there. Basically, tell us Ren and Nora's backstory a lot earlier, even if they don't go into detail. Try harder in showing that while the cities are 'safe places' and thus people born and raised in the city are much more relaxed, that outside the cities things are a lot more tense and harsh.
Speaking of happy endings though, I don't think Juane deserves one. Not yet, anyways. I certainly don't think Pyyrha deserved one. Juane has a lot of growth to do still, growth that almost requires Pyyrha to die/be crippled. And said death or crippling basically precludes Pyyrha from having a happy ending.