The camaraderie and esprit de corps of the channel's news team kept Barry in place when she could have gone elsewhere, the source told the New Zealand Herald.
Her departure after 23 years follows the loss of some of the channel's longest-serving staff - and the associate says many of the reasons for Barry's long-time loyalty have already left the broadcaster.
"She has watched as key journalists, presenters and teams of people she respected and admired [have been] axed, pushed or resigned because their jobs had become untenable."
It is almost a year since Barry cried on screen at the departure of John Campbell after his flagship current affairs show Campbell Live was axed.
The loss of the show saw not only Campbell but other familiar, long-serving faces in the news and current affairs team leave.
And it wasn't the end - Barry has since watched a string of other long-time colleagues go. Newsreader Carolyn Robertson is among them, as is sports presenter Hamish McKay.
The channel has seen the departure of Paula Penfold, wife of Barry's co-presenter Mike McRoberts, and the rest of the 3D investigative journalism team, including Melanie Reid, Phil Vine, Eugene Bingham and Sara Hall. Terrence Taylor - a long-serving and respected current affairs editor - was also a casualty.
The February resignation of Mark Jennings - regarded as one of the safest and slickest editors in a generation - came after 10 months of overseeing the departure of journalists he had worked with for years.
For Barry, the departures included those less publicly known. News producer John Hale left his key role on the 6pm new broadcast - a two-decade veteran close to Barry who travelled with her to South Africa to cover Nelson Mandela's funeral.
The trusted associate said: "The public only ever hear the PR spin, not the truth about those who have left or been axed, because any payouts include confidentiality clauses."
News chief Jennings' departure and now Barry's was a nightmare scenario for MediaWorks.
"There are times in the past Hilary has turned her back on big-dollar offers but chose to stay with the TV3 team she knew, respected and loved.
"I guarantee Hilary leaving MediaWorks is not about any offer of money. It's about the fact the place has been shredded of great broadcasters and journalists, many of whom she has spent much of her career with," the source said.
Those who have worked at MediaWorks have spoken of its underdog role in broadcasting as drawing from staff efforts beyond the call of their paypackets. The New Zealand Herald was told by former staff that employee goodwill - staying late, working weekends and holidays - had largely gone where it had previously buoyed the company's balance sheet in a way that was hard to put a dollar value on.
A MediaWorks spokeswoman said the firm was making no comment beyond wishing Barry well and thanking her for her service.
Chief executive Mark Weldon said: "This was a personal decision made by Hilary. We are disappointed to lose her but also acknowledge that, after 23 years, it's very reasonable she might wish to make a change."
