be a shadow of (someone's or something's) old self

To be dramatically less healthy, vivacious, or robust, often following some traumatic event or negative circumstances. Sharon was a shadow of her old self after battling such an aggressive illness for so many years. This town is a shadow of its old self after so many of its residents have moved away. The company used to be at the top of the industry, but after years of bad decisions and poor management, it's little more than a shadow of its old self now.