Yes there will be numerous resignations and retirements. The ranks of the lobbyists will swell, but they are thick as gnats already so the marginal change will be insignificant.
There will be some worth keeping. Zinke is utterly methodical so those worth keeping have likely already been identified and will stay and thrive at their new jobs.
FWIW, I bet Zinke knew in detail how he wanted to shake things up before he even took the job. Which is why our President hired him.