There is nothing bad I can say about Jeff Hafley and his decision to take the Boston College position. Good for him and his family. I'm just a thinking that we lose more coordinators than a little bit. That seems to be a price for success that we pay that Clemson doesn't pay. Brent Venables has being there since 2012 and I would argue he's one of the best in the game but he isn't named Everytime an opening comes available..
Those that follow Ohio State know that the defense took a huge step back after Chris Ash left. While he wasn't successful at Rutgers he was masterful at the coordinator spot for us. The other shining example is Tom Herman who left after 2 years.
Anyone that has led an organization knows that your people (human capital) is the largest reason for success and the high rate of churn can negatively impact productivity. It is a wonder how certain programs especially Ohio State and Alabama maintain a high level of success in spite of the churn.

Penn State lost Joe Morehead and now Ricky Rahne as OC within the last couple years. I don't think Ohio State has much to worry about as they can essentially get their pick of who they want. It's a good problem to have. Showing you can get people head coaching positions from coordinator positions will make you an attractive spot for an aspiring coach so it shouldn't be too hard to fill the position with a great candidate. And it is never a bad thing to bring in someone new who has fresh ideas that could teach the staff new things or have connections to recruiting a new area.