The parking lot is used for airport employee parking, as several years ago the remaining employee lot in front of the terminal was converted into a premium park and ride lot.
As for the hangar, the only known interested party was UPS, who thought about taking it over not too long after NW
closed it and turn it into a sorting facility. Nothing ever came of it, as there's a lot of hazmat issues with the hangar building that would need to be addressed, and that won't be cheap. There's a lot of asbestos in the complex that would need to be taken care of and I believe there is some toxic waste issues as well. AirTran was offered the hangar but said it was too big for their needs.
I know the apron in front of the hangar is used for the parking of spare a/c by several airlines, and years ago I remember the City of Atlanta PD
using the parking lot as well as the apron in front of the hangar for motorcycle and cruiser training.