Question: How is the now vacant retail space to be re-purposed in the future? The existence of these veritable caves attracts only vermin, transients, and potential pockets of mischief like arson and guerrilla warfare gangs.
Bulldoze them to the ground, cover over with reclaimed sewage sludge, and plant them to bramble and thistles.
I think you're years early here. There's a tipover point of emptiness below which a mall becomes unprofitable. I'm not sure where it is... maybe 15 to 20% unoccupied stores. Most malls I've seen aren't there yet. More likely, new entrants with new concepts will come in and fill the empty slots, at least for a while.