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The presenter is tipped to receive a golden handshake of more than $500,000 when Close Up ends on November 30.
Sainsbury did not return calls and TVNZ has declined to comment on the review affecting Close Up staff.
But Sainsbury has said he will definitely be leaving TVNZ after 31 years.
TVNZ has been scolded by politicians for its generous pay to celebrity presenters, but a former executive says a $500,000 payout would be less dramatic after 31 years' tenure, and in any case it would be incorporated into the cost for the new 7pm show.
Pippa Wetzell has has been tipped for that programme.
An employment law specialist at Duncan Cotterill, Scott Wilson, said payouts varied by seniority, length of stay and salary, but aiming for the equivalent of six to 12 months' remuneration was a rule of thumb.
Mr Wilson said an amicable, "closed-door" exit agreement was the "way of the world" to avoid an ugly termination process with senior employees.
And after 31 years, Sainsbury would have been near the top in terms of seniority, justifying a bigger payout.
"After 31 years' experience, he must have been getting close to retirement. That might be an unfair thing to say of him, but what I'm saying is that the older a person is, it increasingly becomes a consideration."
Meanwhile Sean Plunket will leave his NewstalkZB radio show at the end of the year.
He is understood to be joining rival talkback station RadioLive - reportedly to replace Michael Laws.
Additional reporting Michael Dickison