Science:
I don't think that this is an extinction-level event. It's pretty unlikely that a virus could kill off every seed-bearing plant on Earth. I mean, there are a lot of seed-bearing plants, and not all of them are that closely related. That's a lot of different genomes to mutate into. Viruses don't do that so easily. Keep in mind, for example, that HIV has been crossing over into humans for a long, long time - certainly longer than we have been aware of it and trying to do anything about it - and we are still here. Some humans are resistant to HIV, so they can get it, but never get sick. Some humans are straight-up immune, and the virus can't get a foothold in their body no matter how often they're exposed. Sometimes, immune systems fight it off and the exposed person never seroconverts. Some people just get lucky and never get exposed.
The problem is that because we have modified so many seed-bearing fruits through old-school genetic modification - that is, breeding - we've limited the genetic diversity of many of the species we rely on, which makes both crossing over and infection more likely. While corn, wheat, and domesticated nightshades (and good riddance - eggplants make me sick) might be doomed, I guarantee that wild corn, wild wheat, and actual nightshade flowers will be fine. There might be a genetic bottleneck, but give it a hundred years and the biome won't know the difference. That's what genetic diversity is for.
What we're facing here is a civilization-destroying event. Human civilization is based on the ability of agriculture to produce an enormous amount of food via (old school) genetically modified plants. If we lost that ability because our weird not-actually-fit obscene-amount-of-food-producing domesticated plants went extinct, it's not that humans would die out, it's that the carrying capacity of the Earth would drop dramatically for a couple of hundred years. Some humans would starve, others would die in unrest, but enough of us would survive to carry on.
Which is not to say that our narrator hasn't got significant reasons to be afraid for his daughter's life.
By the way, I think it's important not to overestimate how bad this is, even given what I've said. There are so many ways around this. Find a wild variety that's immune and cross it with the food-producing varieties we rely on. Get big-ass vats of cloned plant matter going. Or, hell, it wouldn't be all that hard to find or produce a microbe that can process raw materials into carbohydrates and other stuff we need and turn that into food. What do you think vegemite and marmite are? And although us Americans find them unpalatable, they are incredibly healthful foods that do not rely on seed-bearing plants.
/Science.
Story:
I loved this story on so many fronts. I loved the stay-at-home dad who wasn't presented as either a tragedy or some kind of defective human being. I loved the slice of normal life against the backdrop of rising chaos. The story did a really good job of getting me to love this little family and dread what's coming.
And, of course, it was beautifully well-written and perfectly paced.
/Story.
