The problem with tunnels is that they have to open at ground level somewhere. If the Israelis occupy all of Gaza City, they don’t have to fight in the tunnels; they just have to seal them. The militants will then die quietly and miserably. Nobody will even notice when they’re gone.
Of course, the problem with this tactic is that the hostages are in the tunnels, too. In a short period of time, I expect the focus of the occupation to turn from military action to negotiations over the hostages and the trapped militants. How many militants per hostage will be permitted to leave Gaza for Lebanon or some other friendly country? We’ll see.