We know this isn't a fairy tale, but the movie really does tie everything up into a beautiful "happily ever after" package.
John has managed to keep his delusions at bay well enough to keep working and stay married, and we've just watched him receive the freakin' Nobel Prize for an idea from his graduate work, which upended economic theory. In his speech, he waxes all sentimental about Alicia and how he never could have done it without her, and judging from the look on her face, it seems like she feels like all the hard times were worth it for this moment.
Schmaltzy? You bet. Much more romantic than the Nashes' real lives? Almost definitely. But this is a movie, and a happy ending is a happy ending—and we'll take those when we can get them.