The city falls after the walls are breeched and the officials of the king of Babylon came and sat in the middle gate.
It would seem that there are still pockets of resistance within the city, but by sitting down in the middle gate these officials were showing that they had authority over the city and its people1. This would seem to fulfill what the Lord said to Jeremiah when he called him as his prophet (Jeremiah 1:15)2. When Zedekiah sees the officials sitting in the middle gate, he realizes that total Babylonian occupation of the city is inevitable and so he and the soldiers with him flee from the city.
3 Then all the officials of the king of Babylon came and sat in the middle gate: Nergal-sar-ezer of Samgar, Nebu-sar-sekim the Rab-saris, Nergal-sar-ezer the Rab-mag, with all the rest of the officers of the king of Babylon.