Father Tom Brennan, 74, died on Sunday at the Hunter Valley Private Hospital after battling cancer for several years.
The priest was the first member of the Australian Catholic clergy to be charged with covering up sex abuse by another priest and was also charged with sexually abusing a young boy.
He was too unwell to face Newcastle Local Court on a total of 14 charges last Tuesday.
"It's going to be very difficult for the victims who thought they would be seeing the perpetrator who covered up another perpetrator being brought to justice," she told AAP. "Having waited all these years, the victims are going to feel robbed, potentially, all over again."
While school principal at St Pius X in Newcastle, Fr Brennan allegedly failed to disclose child sex offences by a defrocked priest, committed in the late 1970s.
In August he became the first Australian Catholic priest to be charged with concealing the child sex crimes of another priest.
He was also accused of assaulting two boys by caning them when they reported sexual abuse and charged with eight counts of sexually assaulting a boy aged between eight and nine at a Waratah church in 1984 and 1985.
NSW Greens MP David Shoebridge said he had spoken to one of the alleged victims, who told him of the priest's death.
He said it would be difficult for victims to deal with their feelings about his passing.
"It will lead to very complicated emotions for victims, which for many will take time to assess," Mr Shoebridge told AAP. "But we cannot allow the church to simply bury its past.
"This shows the urgency of needing to investigate these claims."
Fr Brennan later served as vicar-general of the Maitland-Newcastle diocese, and continued to work as a parish priest in the Lake Macquarie area until as recently as last year.
Representatives of the Catholic Church in NSW could not be reached for comment.