They'll talk. Your typical career federal employee simply won't risk his or her own lifetime credit rating and employability.
They will talk.
And the agency heads can't fire them all.
I'd go through the materials they have on hand at the committee and begin identifying some of these lower ranking career employees and just drop a subpoena on them OVERNIGHT. Begin the hearing on THOSE PEOPLE instantly.
Everything takes time. It cannot be done instantly. Issa is working on it. His committee just demanded all the emails involving all of this from a dozen of the top people. The lower you start, the longer it takes.
We already have a number of GS13/14 types working with the investigation, or so it appears to me.