If malls continue to shut down and decay over the next twenty years, someone should turn them into retirement communities for GenX and Millennials.
Imagine apartments built into what used to be department stores, (Oh, you're JC Penny 203? I'm at Sears 106). Get those old arcades up and running. Set up meal stations at the food court. Once people actually live there, stores will start to move back in.
If I'm unable to finish my life in my own home, that doesn't sound like a terrible option.
As is often mentioned, the plumbing situation makes this somewhat untenable.
But, as the world warms and outdoor recreation becomes impossible, I think they could be repurposed into indoor recreation centers, not that different from a regular mall, just less focused on shopping and more on fun and exercise.