Yeah, the more we talk about it, the more the whole aboveground part really works for me. They coulda pulled their punch and ended on just the burning cityscape in that sort of "oooooh, cooooooool" hollow sort of way, but instead they followed through. They didn't half-ass it and check-swing, they went for it, and made it the culmination of her character arc throughout the movie, using the sequence as a means to pay off all that growth she'd made as a person from the beginning of the film. That it happens while also fighting off a giant alien fumigation ship that spits out wormdogs from outer space could be seen as "corny" or "cheesy" or whatever but I think that it felt more honest and risky than simply going for the cheap "cool" ending that allows people to front like you can't somehow have legit alien action movie bullshit and suspense filmmaking and solid acting/characterization all at the same time.
I appreciate that the filmmakers gave the audience a little more credit than to cut the last 10 minutes of the movie off and shortchange themselves and their characters for the sake of appealing to limited imaginations who can't fathom the idea of a movie being more than a safe genre exercise.
Of course, I guess the counterargument there would be that the last 10 minutes are the safe genre exercise, but to me, there's nothing low about that last 10-15 minutes, and it doesn't seem incongruous to what came before, either. The two are glued together really nicely, for me. The stuff belowground flows into what happens aboveground really fluidly, and the stuff aboveground pays off what happened below.
Cutting it off as she gets outside, it's the story of how this girl escaped John Goodman. Letting it play out to the end, it's a story of how a girl triumphed over John Goodman, and Alien invaders, and her own shortcomings as a person.
I prefer the latter. It does more.