It's not as if he's dealing with unfamiliar players, a big loss of senior talent, etc. He has most of the offense back for 2020, and especially having a veteran QB the likes of Book allows him to stay in his comfort zone.
If the offensive line can stay healthy (they were a wreck this year, looking more like an infirmary), and if one of the running backs can step up to be "the man," then I see no reason why we can't have another 10+ win season.