Acting DNI and Trump will refuse. Schiff will issue subpoena. Acting DNI, at Trump’s (perhaps unspoken) direction, will refuse to comply with subpoena. Schiff’s committee will sue to enforce the subpoena. Barr’s DOJ will file a motion to dismiss saying it’s an inter-branch political dispute and the courts cannot get involved because … something, something … we have to protect Trump.
We need, not only whistle-blowers, but people with documentary and taped evidence who are willing to leak those things to relevant committees and the media. It may be the only way to get any look at what is really going on. The next Democratic president can pardon them all - ETA: while prosecuting the Trumpers.