What in the world does "seal up the rubble in the city too" mean? I presume the panel shows the remnants of Webinar's camp... or is Parson destroying the city between the Outer Wall and the Garrison Wall?
That was the camp inside of Gobwin Knob's walls where Parson's forces were the night before. Sizemore said that collapsing the tunnels might collapse the entire city... Just goes to show how good Sizemore is, and how serious they are about winning.