Board Thread:Skyrim/@comment-101.164.107.138-20141130063846/@comment-25528618-20141130112821

Did you side with the Imperial Legion? That could possibly explain why, since Hemming will become Steward to Maven if you side with the Empire. Which also wouldn't make sense since you can kill any other Steward so long as they don't play an important role, which Hemming, in a way does not. You can also kill Sibbi if you use his cell glitch but the guards won't yeild.

Hell, it might just be a glitch. If you want him dead then you could use console commands to make him non-essential, assuming that he is and if you're playing on the PC.