Those dead brown larva tells the story for me. I've seen it once before on some brood that was in a piece of burr comb pulled from one of my hives just a week ago. It is from starvation. The one thing I didn't see any of was pollen and nectar/honey which they need to rear brood and keep the existing bees alive. Looking at the bottom board with all the dead bees I see the entrance reducers are both turned to be completely closed off. Was this intentional or after the fact? Reason asking is it could also be due to that Heat kill. Is the queen still alive?