Police found no evidence that "foul play" contributed to Annabelle Tumanako's disappearance, a court heard.
The 35-year-old was last seen at her Napier home in June 2007.
At an inquest today, coroner Peter Ryan ruled that Tumanako was likely to now be dead.
However, due to a lack of "clear evidence" he could not determine if she deliberately disappeared, committed suicide or someone took her life and hid her body.
During the inquest detective sergeant Emmet Lynch said there was no evidence to suggest foul play contributed to Tumanako's disappearance.
Tumanako suffered from a schizophrenic illness. At the time she was living under a mental health community housing programme in Maraenui with two other people, including her boyfriend.
He was the last person to see her alive.
Tumanako's case worker had visited the couple that afternoon and gave them $17 to fill up her empty car and dropped them at the car in Maraenui. Tumanako returned home with her boyfriend of five years and went to bed with him that night.
She and the car were gone in the morning, the inquest heard.
Police investigated Tumanako's boyfriend who was known to be violent but found no evidence to link him to her disappearance.
Five days had passed by the time Tumanako was reported missing by a mental health worker.
Police conducted an extensive ground search after Tumanako's car was found to be abandoned outside the Westshore Hotel.
The car had run out of petrol.
No items of clothing were found nearby on the foreshore and there was no evidence to suggest she had been taken against her will, Lynch said.
It was out of character for Tumanako to disappear for a long time without contacting family members. She had five children which she frequently visited, the inquest heard.
Tumanako did not have a cellphone or passport and had not accessed her bank account.
Lynch said it was unlikely Tumanako would have the resources to deliberately disappear or to survive on her own.
The coroner ruled that Tumanako died on or shortly after June 23 2007 at an unknown location.
It was possible she walked into the sea to end her life, Ryan said. However, her father Jo Tumanako told the inquest he doubted his daughter would take her own life.
He said she hadn't been herself the day before she went missing and talked about going away.
Ryan said he was in an "unhappy situation" with very little evidence and apologised that he could not offer the family more closure.
Nevertheless, her father was happy the inquest had taken place.
"They've done all they can," he said outside of court.
He had suspicions about what happened and firmly believed his girl was taken.
He still holds out hope of one day finding her remains.
Time hadn't lessened the pain, he said.
"It's been tough."
- The Dominion Post
How many coffees do you have a day?Related story: Coffee as we know it at risk of dying