While bees here in the US had not been exposed to mites and the viruses they gave the bees, many did die as a result. however,those that were able to survive the new parasite began to pass on whatever genes gave them this advantage. Even if they were not robust,they survived the onslaught.
just as not all humans died during times of plagues and disease, some of the bees survived. Likely there were also some feral colonies of Russian bees too which may have had a history of mite exposure. But there definitely was a sharp decline in feral and non feral bees. I think with the news of CCD there was a surge in new beekeepers that may have also contributed to feral populations through newbee management practices.Or some just didn't worry about swarm control and left the bees do what they do naturally.
But either way it happened,bees are slowly recovering. The colony losses are decreasing to the twenty percent range from thirty five percent and more.