Boyle redeemed the sport's reputation with a gold medal in the 800m freestyle and a bronze in the 400m freestyle at the 25m short-course world championships in Turkey last month.
The 25-year-old also led the New Zealand campaign at the London Games with two finals appearances, the only Kiwi to progress that far. She finished fourth in the 800m final and last in the 400m freestyle final. Breaststroker Glenn Snyders - also mentored by Regan - was next best, making the 100m and 200m semifinals.
Boyle is on a government performance enhancement grant of $47,500 over the coming year. She is believed to be keen to race until at least the 2014 Glasgow Commonwealth Games. However, a significant proportion of the $1.4 million was expected to be channelled towards what she wanted to do. Her influence may be less certain now her coach is gone.
News of Regan's decision coincides with tomorrow's arrival of new high-performance director Luis Villanueva from Spain. A call on whether Regan was to be retained as part of the coaching structure had been expected to be one of his first jobs.
O'Connor said the board would make a future coaching decision only after consultation with Villanueva.
"I'm looking forward to working with Luis but I'm not in a position to discuss what we do until I've talked to him," he said.
It is understood Regan's swim squad had been hoping last month's departure of fellow high-performance coach Scott Talbot to the New South Wales Institute of Swimming and Sydney University would free up budget to retain Regan.