Kerrigan is very much in the mold of Orakpo in that both were pass rushing DEs in college. So, Kerrigan can get help from Orakpo in making the transition.
The difference is that Kerrigan is supposed to be better at stopping the run than Orakpo.
As far as Rocky, I too believe he will be gone. Either Henson or Riley can fill that need.
The question is, with Kerrigan in who backs him and Orakpo up?
We had Carter, Wilson, Alexander, and Jackson as the opposite OLB. All are converted DEs and none made the switch well.
Jackson showed some flash, Wilson was servicable, Carter was horrible (as expected), and Alexander was often lost (despite his effort and heart). Carter is gone, and I think Wilson and Jackson have the inside edge on backing Orakpo and Kerrigan up.
So, where does that leave Alexander? He is not, and cannot be and OLB in a 3-4 scheme. He is too small to be a NT or a DE in a 3-4 scheme. Could he be an ILB in a 3-4? With Rocky going away, and Henson and Riley stepping up, does Alexander have a shot at being a back-up ILB? If not, where would he go?