George Miller is apparently in pre-production on Mad Max: the Wasteland and has Hardy signed up to do two more Mad Max films. I expect they will be finishing the script and building a monstrous set design even before Hardy is signed on.
Tom Hardy spoke to Esquire and had this to say when asked if there will be a sequel:
"Yeah I believe so! I don't know when that starts, but I believe that's in the books. There's a couple of those floating around. I'm waiting for the call to come. It was so good, man."