Why would he fire anyone?

He's not running for reelection, so he has no one to answer to.
If he fires someone, then their replacement might have to go through a congressional approval, which means pain and suffering. For what?

And as long as these people are in place, it will give a target, which means one less person attacking the chimp in chief headon.

The only way of of these people will be gone is if they quit because they can't handle the hearings, or if someone find a smoking gun (ala Goodling) and they have to get out of the limelight or even worse things will happen.