The fate of the hostages aside, a good strategy would be to bury Hamas in the tunnels. Block every exit.
Or pump in an overkill amount of aerosol vomiting agent into any found tunnel...
I would assume that several of the entrances/exits to the tunnels have already been blocked over the last couple weeks.
When you blow up a multi story concrete reinforced building the pile of rubble would cover the entrance.
I would think the entrances still in tact are under the hospitals, schools, mosques and churches.
Fill Gaza with sea water.
Most of it is well below sea level.