It would also have to remain viable in the sense that no animals starving in the darkness will try to eatthem, or fungus or bacteria running wild. I think you have to assume that are small burrowing ancestors ate pretty much every seed they could get their tiny paws on. We know that quite a few different organisms survived, and while some of them estivated or hibernated most of them presumably we had to live and eat in a roughly normal way.
Fungi and bacteria don't like the cold. There would be a lot more food to eat for survivors (chickens) as things that they competed with for food (T rex) died off.
