it take for a bp to starve to death? or better yet, will a bp starve to death? does its instinct to survive kick in at some point and make it eat?

Long story short, goliath still hasn't eaten, has lost some more weight, but he received a clean bill of health when I had taken him to the vet. I've put a call into the vet again and he should be calling me back tomorrow. I'm just about ready to assist feed, but not sure if I should yet. he is in a 15g long tank, temps & humidity spot on, two identical hides. He does not show any signs of an RI so now Im totally confused. any advice is greatly appreciated. thanx.