I'm not aware of stats, but there is a general description:
A magical obsidian object (CL 15) about 70 feet high.
This would give it saves of +9, and hardness and hit points like a stone object (DMG 214).
Stone has hardness 8 and 15hp/inch of thickness (PHB 166).
We are not told how thick the statue is. The map of the temple suggests 15-20 feet, though, and that sounds about right for a 70-foot tall statue. That works out to 2700 to 3600 hit points.
One could be generous, I suppose, and let them attack, say, a leg, and destroying that causes the statue to topple, with much ensuing mayhem.... A 5-foot thick leg would have 900 hit points.
