Maybe we will win miss the playoffs next season, Joe will have difficulties leading the Team that he hasn't had to this point, and it will make sense to bring on another manager.
However, that's not the case yet, so Joe will be back as manager next year.
Clearly, Theo expects more in 2019, which is fine. If Joe and the Cubs deliver, Joe will likely get extended. If not, it won't surprise me to see Cubs go another direction...but we aren't there yet.