If Mike Tyson hadn't fired Kevin Rooney how long would he have stayed Undefeated?

Mike Tyson fired Rooney after arguably his most dominant performance against Michael Spinks. I know that Tyson would have been a better fighter if he had kept Kevin as his trainer. After all would Muhammad Ali have been the same with out Angelo Dundee? So if Rooney had stayed with Tyson how much longer would he have stayed undefeated? Would he still have lost against Buster Douglas, or would his streak have continued well into the 90's?