I've read a lot of predictors say that had Miles stayed, some might be more inclined to have picked Missouri with how the LSU season was going.
I'm not sure the loss of Fournette is necessarily the bigger issue, as Missouri held Chubb to 63 yards on 20 carries. Missouri's bigger defensive issue seemed to be their pass defense, and if Orgeron's style change gets that passing game going, that could be the decider (he did go, what, 6-2 over the rest of USC's season as an interim).
Mizzou's bigger strength is their passing attack, but last week showed their young QB has a bad habit of forcing his throws and their offense doesn't take up a lot of time / isn't on the field very long, scoring or not (not to mention a meh running game). Point being, if they're not scoring, their defense will likely be on the field a lot...not a good thing for later in the game.
I think the loss of Fournette is less a concern than how well Missouri's QB can handle LSU's defense and what - if any - changes Orgeron's coaching might make for that offense, especially passing the ball (he did go what, 6-2 at USC after Kiffin left).
Of course, if Mizzou goes pick-happy again, it's probably easily LSU's game.