Just think of the leaks that will come out then!
Manafort and Don Jr. can talk freely outside of the hearing, about what happened inside the hearing. Neither of them come to the hearing with any classified information. Anything they say, anything they are asked, all of that can be reported if they want to.
Manafort has some very strange and complex financials dealings.it takes awhile to unravel all of those shell company transactions.