greenbtree, nice to see another Iowan on here! I'm about 190 miles from you. My first reaction would be that the hive that is dead or near-dead, doesn't have enough food. I haven't done any requeening myself at all, so I have no basis on which to voice any opinion.
Leaving the swarm cells to the old hive and starting another seems like sound advice to me, as long as you have some frames of brood with some bees on it to spare. But certainly leave the candy plug in your queens cage. It takes them a while to chew that out. By then, they will likely have come to accept the smell of the new queen as their own.
I'd put some mason jars of sugar water (2 parts sugar 1 part water, dissolved well) with nail holes in the lids upside down, inside an otherwise empty super on them. Then put the outer cover back on. It has been nasty and cold, but if they're starving, it's not gonna get any better for a while. When this rain finally lets up, it's still gonna be a bit before the pollen and nectar are fit to provide food for them again. Feeding them can't hurt.