Rap God was an epic tune and one that I thought signified that he still had loads to give. But as you say, he's 45 now and as Em himself once said to Ray Benzino; 'nobody wants to hear their grandfather rap, nope'.
For me it was amazing that he was still good after the first 2 albums. They were so full of anger, that I remember thinking; will he be any good when he's not so angry anymore?
As to whether he's fallen off, never to return, only time and crappy album sales will tell :-)