I can speak first-hand about abdicating during a rebellion. You get instantly banned and declared a rogue, and by extent lose your Royal status. Once you know you can't win it's basically a fast-forward button to the end of the rebellion.
Still a nice big "FU" if the rebels were hoping to reform the government.
Never felt right to me that the deposed ruler had that power to decide if the rebels could or couldn't reform the government...
