FYI, this is the current situation in Gaza.
Israel has stayed away from invading the main population centers because Hamas is fully set up for massive ambushes and counter insurgency.
If they REALLY want to conquer all of Gaza and occupy it, they will need to be prepared for many more casualties. They have sustained about 1,000 troops killed and 10,000 wounded; I could see easily 5x more of each if they try this.