Deportees
After the Assyrians won the siege, they deported the population. We can see the people moving in a long line while carrying their belongings. This line was continued along the lower edge of the relief but has since broken off. We also see Assyrian soldiers impaling prisoners.
The deportation of populations was standard practice in Assyria. It was a way of dealing with troublemakers and generating cheap labor. Moving so many people must have been a logistical challenge, but the Assyrian army campaigned so much that they managed to perfect the deportation to an industrial efficiency. The closest modern-day equivalent would be Stalin's deportations in the 1930s. The main difference is that on the relief we see the refugees carrying their possessions and cattle, whereas Stalin would force refugees to leave everything and then drop them off in the middle of the desert. So compared to Stalin, Sennacherib was kind.