A Senate estimates hearing on Monday was told that Dr Parkinson had informed Mr Turnbull he was dropping the previously undisclosed investigation, saying there was "little to be gained" from continuing in the wake of the former Nationals leader's resignation last week.

Facing lengthy questions about when Mr Turnbull and senior ministers first knew about the affair and Ms Campion's subsequent redeployment to two other Nationals offices, Finance Minister Mathias Cormann told the hearings Mr Turnbull had ordered the investigation with Mr Joyce's cooperation.

A separate investigation into Mr Joyce's travel claims and other spending related to Ms Campion was also revealed, and that probe by the Independent Parliamentary Expenses Authority will continue.

Senior government sources suggested the authority initiated its inquiry, and officials from the watchdog are expected to be grilled at estimates on Tuesday.

Chapter to be written by Barnaby

Meanwhile, Mr Joyce's supporters have left the door to him one day resuming the leadership if he can rehabilitate his reputation during his backbench exile.

"Who knows what the future holds? If you had said to me four weeks ago he wouldn't be deputy prime minister any more, I would have said you were crazy," NSW Nationals senator John Williams said.

"You have to wonder," another MP said, when asked whether it was possible for Mr Joyce to be resurrected.


"If things go his way, I think what we will find his popularity will cause a call to come back," the MP said, suggesting Mr Joyce's replacement as Nationals leader, Michael McCormack would have to keep forces at bay.

Nationals federal president Larry Anthony said he believed Mr Joyce still had a role to play in Parliament.

"That chapter is to be written by Barnaby," Mr Anthony told Sky News.

"What I'd like to see as president of the party is that he rucks in, that he supports the team, that he still remains that fierce advocate for people in the weatherboard and iron as he so articulately puts, and I think he will continue to play that role."

Even Mallee MP Andrew Broad, who on Thursday demanded Mr Joyce quit, offered a charitable comparison to Winston Churchill's wilderness years.

"We all learn from our experiences, perhaps we all come back empathetic as a result," he said.

"I think that would be a great story to tell but then that's a choice for what Barnaby chooses to do with his future."