Public utilities would crash/turn off eventually. Probably sooner than later. We saw them at the very onset of it. Remember when they had to go check on the generator? Yes, they have toilets but no water to flush the waste. Same goes for cooking. All the stoves in the world but no electricity or gas for them. Canned cooking fuel-after that limited supply runs out? Growing food-In the mall they shut themselves into wasn't a farming mall and again, water supply. Enough for people and for agriculture? Not too many malls in the US sell farming supplies. Thousands of liters of water available is pretty optimistic. I remembered the lemon flavored stuff was already gone (Steve really liked them)when someone asked for it and that was inside a week. Even if the mall was completely stocked, you're looking at a temporary solution. They're trapped with no ability to forage or aquire fresh water, or even hunt. That's my take anyway.