He and agent Noel Mouldey believed having consent to demolish would make the property more attractive to potential purchasers.
However, on Thursday, Mouldey confirmed that the building had been sold privately to a local purchaser.
"It's a real weight off [Karantze's] shoulders," Mouldey said.
"I have no idea what he [the new owner] intends to do with it."
Mouldey said he was unable to disclose the name of the new owner who would take over on October 31.
The Thain's building is a Class B heritage building in the Whanganui District Plan but has no national heritage status.
The three-storey unreinforced masonry building is severely earthquake-prone at 5 per cent of new building standard (NBS) and the ground floor was flooded in the June 2015 floods.