Could this be a better ending?

For a meteor of that size and velocity, the ash cloud would have lasted years if not decades.

But regardless, I think a far better ending would've been to have them emerge out of the bunker after more than just nine months - John and Alison are a bit grey now. A man runs up to them, out of breath, holding a baby, and says "Sorry, I tried to settle [child] before I came up here". John puts his arm around him and responds "I'm so proud of you, Nathan".....or something to that effect.
I just think that nine months isn't a long time and the ending was lacking impact. But that's just my opinion.