I have had a hive swarm (I watched it go), and then when I went into the hive, there were queen cells and there were eggs and young larvae.
It may have swarmed. If you leave it, the hive _will likely_ swarm (assuming those were actual queen cells - they were more than 1/2 inch long, right? Had white goo in them?). If it does swarm, it will likely produce multiple swarms, the first headed by the mated queen, the second and maybe third by virgin queens, 5-8 days later. This is to be avoided. More on that in a sec....
I have found some hives will swarm no matter how much room you give them. So, the backfilling could be an indicator that this hive is going to go. Typically, I see nectar and honey stored on the combs in the upper parts - or on combs 1,2 and 9,10 (if you have double deeps). There are always central combs - at least 2 - with no nectar in the center so the queen can lay there, if they won't be swarming. ANd the rest of the combs (except those with honey/nectar on the outside) will have brood in the center. So nectar in the center of the combs, that are in the center of the brood nest, means the bees either ran out of room to store, and will now swarm, or have decided to swarm, and will now swarm. I have found a massive disruption of space, such as replacing 8 frames with undrawn foundation, will help dissuade the instinct to swarm.
What should you do? Well, if you can split the hive, leaving 2 queen cells in each split, you can guarantee the hives won't afterswarm. One side will either tear down the queen cells and have the queen resume laying, the other will be on a track to have a virgin emerge, then do her flight, then either never come back (25% of the time, in a good apiary), or come back mated.
If you split the hive, make sure the one with the foragers is given either an undrawn deep, or drawn or undrawn supers. They will have lots of bees emerge, no brood to take care of, could bring in a lot of nectar - give them space to work! Not sure if your area has much nectar coming in, but it sounds like it if you are seeing a lot of nectar in the brood nest.
Make sure the other half has pollen patty, or give them 3 combs with pollen on them, and maybe feed 2 quarts. They won't have foragers for 10-14 days and that is a problem for raising strong young bees. You can always recombine these once you get a mated queen back.
I would not leave the hive to its own devices. I haven't found miracles to be that common in beekeeping.
there are steps you can take to help this hive succeed at overwintering - not losing half the bees and not risking going queenless are 2 big barriers to overwintering that you can hopefully prevent.
And... there are some dates you MUST make a note of.
7/21 open queen cells, larvae, eggs. (you have 3 weeks from this date until the hive is a laying worker hive, if the hive swarmed, and the virgin queen does not return).
so... projecting into the future....
7/29 possible virgin queen out (8 days after capped)
8/2 mating flight
8/6 earliest eggs
8/16 earliest capped brood; getting into laying worker potential here.
So.... some options here. Surest course is to split, remove all but 2 queen cells in both splits, baby the split without foragers, give space to the split that has the foragers. You can always recombine later. Gotta wait to be sure either the hive has a queen and eggs, or...doesn't.
And if they didn't swarm, you'll be able to see that, and recombine sooner. Just realize this "close call" means in spring, the hive will swarm early. late summer-fall swarm attempts in my apiary are a bad sign for being able to keep the bees in the box in spring.