Mostly agree with your percentages. I'd increase the no timeline reset percentage to 90%--at least in terms of a major timeline reset. It's extremely unlikely that the producers would overwrite their own first two seasons. Even if the characters remember the events, they're not going to wipe out the events that they've worked to build up and the audience has followed for several years. To preserve canon, they'll use time travel to get Discovery to the future rather than rewriting the Discovery's past. Trying to guess at the shock reveal. It'll have to be something brief that they can flash on the screen at the end and is shocking on face value. Perhaps encountering an aggressive Federation starship from a decaying era? Not sure.