This was a very fitting ending to a very good series. I do wish there'd be an epilogue showing the others back home when they find out about their deaths, though. And to see what happened to glasses girl
I wanted them to be happy, which granted they are
They are...? But they are dead. And they didn't seem all that happy with how their lives ended, honestly. Though I guess you may be referring to the supposed afterlife scene... I only interpreted that as Hina's final thoughts, a delusion caused by her exhaustion or something. I guess it's left up to the reader, but with the way it was shown, right before showing us their bodies covered in snow, it seems like that was just her wish as she was losing consciousness.
Edit: Btw did Hina go out with the intention of killing herself or did she just gave up after falling?
Seeing how she had been carrying Airi's body for who knows how long, in the cold, while being underfed, with little sleep and under enormous amounts of stress for a number of days, I think its more than likely that she really couldn't get up, even if she wanted to.