That series was written in chronological order so that when Rebus reached the mandatory retirement age Rankin simply ended it. That was a few years ago.
Rankin has just published "The Complaints." This book features Malcolm Fox, a very different sort of Edinburgh cop. Fox works in "The Complaints." His department is the Scottish equivalent of what we would call "Internal Affairs." Fox investigates other police officers.
In this interview Rankin talks about how he came up with this new character and whether or not this might become another series of books for him. And he mentions the possibility that he would consider bringing back the retired Rebus for more books after all.