The AD cannot let everyone jump ship during a federal investigation. That would look really, really bad. I say they keep the rest of the staff for at least next year. That would show that this was just the isolated actions of a disgruntled former player and coach. The program needs the appearance of stability.
Plus, where would Grier go? He is a bad coach who has this hanging over his head.
They also need to immediately hire a damage control specialist who will get out ahead of this story. They need a public statement immediately (no knowledge whatsoever of this happening, we are in total control, we will fully cooperate with investigation, etc.).
If handled incorrectly, that program could be toast.