Makes excellent sense. Although I have heard the tunnels are vast and complex. No telling what it will take to get rid of them. Also, they have machines that make new ones really quick. They have to be destroyed as well.
They can 1) determine there are no living beings in the tunnels, while progressing through them (hostages included, if alive then hard work to get them out, and then, having determined this in each segment utilize sponge bombs which fill all the spaces and then immediately harden to a binary epoxy/hardener compound. 3.) let that sit for a week or so, and then flood the entire system with water containing neutralizer for the compound (there is something that does).
Problem solved- except the degree to which the solvated water filled tunnels will support anything built over them.
So the rebuild would have to be no more than 2 story buildings.