Northanger Abbey has a very neat and tidy and rather clichéd ending: all the nice main characters get married to other nice characters and live happily ever after. All the mean characters end up alone. It's like a Disney movie.
Aside from being rather predictable, this ending is also a little weird. What's odd about this ending is that the entire novel spends a lot of time undermining the various clichés of popular Gothic novels. But it ends with a series of giant clichés, including a deus ex machina, which is a fancy Latin term meaning a convenient plot element that is dropped in out of nowhere. The deus ex machina here is that one of the nice and long suffering characters happens to marry a wealthy Viscount who has never before been mentioned. It's completely random. And the narrator even admits that this is pretty weird and random.
The novel's ending isn't just clichéd, it's totally over-the-top clichéd. So, rather than being out of step with the rest of the book, the ending actually bumps the satire up a notch and goes for broke. Like the rest of the book, the ending is still highly satirical – it exaggerates and mocks the types of sentimental and even ludicrous endings often found in Gothic novels. The ending just accomplishes the satire in a different way than the rest of the book, which relies more on clever dialogue and humorously disrupted expectations. Instead of letting the characters supply the humor through their words and actions, the ending utilizes outrageous plot devices and ironic narrative commentary. Still, why Jane Austen decided to go with an over-the-top ending instead of a more subtle ending is debatable.