The pair camped at various places in the Catlins before Mr Beckenridge’s dark-blue 4WD Volkswagen Touareg went off a 90m cliff near Curio Bay a week later.
Six weeks later police dragged the wrecked vehicle from the water.
The bodies were never found and rumours that Mr Beckenridge staged their deaths have swirled ever since.
Police have failed to solve the mystery and it was confirmed yesterday it would be the subject of a coronial inquiry at the Christchurch District Court in May and June.
Five years after the disappearance of the duo, Mike’s mother, Fiona Lu, told The New Zealand Herald she was convinced her son was still alive.
"I miss him deeply and I am hopeful he will return. I love him," she said.
Mr Beckenridge met Ms Lu while they were working in Afghanistan in 2006.
The couple later moved to Queenstown but their relationship broke down in 2014, shortly after Ms Lu moved to Invercargill to begin a hairdressing course.
While police had followed up on potential sightings of Mr Beckenridge and his stepson in New Zealand and overseas, their inquiries proved fruitless.
In 2017, international child-abduction expert Col Chapman said the evidence led him strongly to believe they had fled the country.
