Board Thread:General Discussion/@comment-67.185.219.143-20170329045317/@comment-36869183-20181113065957

probably way too late, but in theory, you CAN just 'quit' the DB storyline without killing the emperor...you probably wont be able to do any more assassignation quests or interact with most of the members beyond basic idle chat lines and nagging reminders to finish off the emperor, but it should be possible

not sure what would happen if you proceeded through the quest until the face to face with the emperor and just left without killing him, but like Purrington said, if it did let him leave alive, that would entirely undermine the entire point of the DB questline up to that point

also, if you REALLY wanna be sure the emperor survives, just either leave the DB alone (since the dragonborn seems to literally be the only person in this ENTIRE WORLD whose competencies exceed stab here and loot there) or outright turn against them and kill them all to ensure none are alive to off the emperor at the traitor's behest (which I find to be a rather ironic ending to the "moral highroad" variant of the DB questline)