Not necessarily.
Michael Hawkins has experience with 4 starts under his belt & has good mobility as a running QB.
Obviously, he doesn't have the arm talent of Mateer, but the Offense doesn't have to completely change due to the fact he can operate the Mesh point read options in a similar fashion.
He's not likely gonna stretch the field as often, but Oklahoma has good weapons & if he can keep from turning the ball over, Ben Arbuckle can manufacture productivity from the offense enough to win a few games until Mateer comes back.
They also have a really good Defense that will keep them in games enough to give them a shot.