I've read this strategy in other places. Would this mean saving hostages is no longer part of the plan?
It would be wonderful if that could be done.
But chances are most of the hostages are dead by now.
At least denying Hamas the tunnels would mean they can't use them to get in the Israeli rear and put the entire effort in disarray. It would make it far more difficult for Hamas to do pop-up attacks, too.
The alternative is to invade the tunnel system as well, where the home turf advantage is considerable, and if the Israelis get close to cornering Hamas there, the hostages will likely be executed anyway.
I suppose there is always that longshot chance they would try to bargain with them for their own lives, but these aren't normal people anyway, and a lifetime of imprisonment might pale compared to 72 virgins.