In a surprise move, TVNZ revealed it has agreed to an approach by the show's producers, South Pacific Pictures, to write a one-off script. A draft is expected in a few weeks.
But Richards warned this was not confirmation the finale would go ahead.
"There are plenty of ifs and buts, and it's perfectly possible that this won't go ahead, so we don't want to raise hopes only to dash them," she said.
"We've had to disappoint fans once and we'd rather not do it again."
She said the network had to assess the quality of the script before asking NZ on Air for the more than half a million dollars of public money it would take to make the finale.
The network also had to assess it against its own drama strategy. The show would have to make a positive contribution or filming would not take place.
Richards said the series was abandoned because not enough people were watching to it.
The average audience had dropped from 412,000 to 258,000 over the second and third seasons.