But the police department won't say whether he was given a golden handshake to hasten his departure.
Mrs Nicholas told the Herald last night that Mr Rickards' resignation had come as a surprise.
"In a lot of ways, I'm pleased that it's another chapter closed, but I am disappointed that the internal inquiry won't be held. I feel that's where the closure was going to come."
Police would not say what the internal charges against Mr Rickards were, but at least one is believed to relate to claims that he had sex with a woman on the bonnet of a police car in the 1980s.
Other charges are believed to relate to his admission in court that he had sex with Mrs Nicholas, his claim that the investigation into police sex crimes that resulted in his facing charges was "a shambles", and his support for convicted rapists and former police colleagues Brad Shipton and Bob Schollum.
Mrs Nicholas said she hoped Mr Rickards did not get a payout.
"I hope like hell that there has been no golden handshake, no extra payout.
"The guy's entitled to his superannuation, which he's paid into, but anything over and above that, after what he's received over the last four years, I don't think that's right."
Mr Rickards had been suspended on full pay of more than $150,000 a year since February 2004.
In September, he was given a new $50,000 Holden Commodore as part of his remuneration package.
Police spokesman Jon Neilson said the department could not comment on whether Mr Rickards had received a golden handshake.
Detective Superintendent Nick Perry, the head of Operation Austin which conducted the investigation that led to Mr Rickards' court appearance, was not surprised at the news.
Speaking from London, where he is now New Zealand's police liaison officer in Britain, Mr Perry said someone sent him an anonymous text yesterday morning telling him the news.
"I'm not really in a position to comment, it's not appropriate. It's up to people to draw their own conclusions about why he resigned and I'm sure they will."
Mr Rickards, with Schollum and Shipton, was found not guilty in March last year of of raping and sexually abusing Mrs Nicholas in 1985 and 1986.
In March this year, the three were found not guilty of kidnapping and indecently assaulting a then 16-year-old girl, whose name is suppressed, in Rotorua more than 20 years ago.
In a statement, Mr Rickards' lawyer, John Haigh, QC, said his client and the police believed that maintaining the public confidence in the force was of paramount importance.
"As long as this high-profile dispute is allowed to continue it will dominate the headlines and confidence will naturally come into question."
The statement said Mr Rickards denied any wrongdoing, and considered disciplinary proceedings to be without foundation.
"He does, however, recognise the untenable position of him continuing in his role with New Zealand police, and in the interests of all parties has decided to resign."
After his acquittal in March, Mr Rickards widened the rift between him and his superiors by attacking the Operation Austin investigation they ordered into police sex crimes after Mrs Nicholas went public with her allegations in 2004.
"It was an investigation I would have been ashamed to have led," he said. "It was a shambles. And the police need to be held accountable."
Mr Rickards also defended his jailed co-accused, Shipton and Schollum, saying, "They shouldn't be where they are".
A spokesman for Police Minister Annette King said "she is pleased there has been a resolution" but would not comment further.
Police Association president Greg O'Connor hoped the resignation would enable the police to move on from "the Rotorua incident".
"I think most sensible thinking New Zealanders have seen it for what it is - an isolated incident from an era some time ago."
- additional reporting: Claire Trevett, Alanah May Eriksen
Clint Rickards
* 1979 Joins police at 18
* 1997 Youngest district commander at 36
* 2006 Acquitted of raping Louise Nicholas
* March 2007 Acquitted of kidnapping and indecently assaulting 16-year-old girl
* November 2007 Resigns from the police
