I seriously do not think that Ohio State will hurt at linebacker. Guys like AJ Hawk don't ever really leave. It's lame, but his spirit will live on. He's the type of guy who's influence will be felt at OSU 8 years from now.
Spirit is nice, but replacing that kind of talent is not so simple.
You are right, though, Ohio State will be fine. For the same reason all the great programs stay great. Recruiting. The teams that sign top 10 classes most every year are the teams that hang out at the top of the heap. The difference between a good coach and a great coach in CFB is recruiting. There are reasons that head coaches from programs like Ohio State never coach college football again when they get fired. People say if you can win there, how are you going to win anywhere else.
If Mack Brown gets fired at Texas in 5 years, he won't find another job in the college ranks. It won't have anything to do with how good a coach he is, it has everything to do with how good he is as a recruiter.
Joe Paterno all of the sudden forgot how to coach all of the sudden. After 40 years he just didn't have it anymore. Then he plugged in a good recruiting class and he is a great coach again.
My point with Ohio State is that you can't replace 9 guys on one side of the ball and 16 starters in all and compete for the national championship. Ohio State will be rank very high in preseason based on how they finished the year and based on reputation. They will be ranked because of the respect that last years teams earned and they will have to live up to the reputation with 16 guys that didn't start last year. It is a tall order.