Losing a player like Cam Newton in an offense like the laser-guided Wing-T mutation Gus Malzahn runs at Auburn is like losing three players at once. You first lose a running back who accounted for 105 yards of rushing offense a game. Next, you lose the most efficient passer in the country. Finally your offense loses the hybrid factor that made life hell for linebackers and safeties caught in the multiple coverage dilemmas presented by a running quarterback who--with little more than a flick of his wrist, mind you--can loft accurate deep balls to receivers in single coverage fifty yards downfield.
To properly understand the crater-sized hold Cam Newton will be leaving, you first must survey the exact size of that hole.
Cam Newton accounted for exactly 309.7 yards a game of Auburn's 499 yards of offense per game. That's 62.7% of your yardage, but we haven't even accounted for the touchdowns. The Tigers scored 75 TDs in 2011, and of those Newton scored 51 of them by running, passing, or catching the ball for six points. (Yes: he did catch one, too.)
With 68% of your offensive touchdowns walking out to shake Roger Goodell's hand in Radio City Music Hall, Auburn will be diminished in its offensive powers next year. This is a factual statement: if they exceed these, it will be because they find a transfer qb who is later determined to be a genetically engineered supersoldier on the run from the United States military doctors who created him. (This being the SEC, one should not rule this out completely.)
The immense hole left by Newton's departure will be somewhat filled by coaches during spring practices, where coaches inevitably patter on about no one getting the job yet, and all positions will be open blah blah blah. The replacement by depth chart order will most likely be Barrett Trotter, who will be a junior next year but already has one advantage over Cam Newton: he's clearly ahead in Namath Shirtless Hairy Manbeast points.
Trotter runs a 4.6, but he's not going to have the size (6' 1" versus 6' 5") that Newton had or the bulk to absorb the hits Newton shook off like a runaway Brinks truck. (215 or so versus 250 pounds of coiled fast-twitch wonder.) In other words he's like a faster Chris Todd, a good timing passer with the basic ability to run the option to a satisfactory but not spectacular degree. They'll pass a bit more, hand off carries to the running backs a bit more, and watch as they field a quarterback who will come closer to "excellent" than "terrifying in his godlike powers."
Trotter will not be able to be Newton, but remember, the last person to recalculate your understanding of the universe named Newton came around over three and a half centuries ago. A regression to the mean isn't just inevitable, it's essentially a matter of historical fact.