Jeannie,I hate hearing things like this. As you know,the reason he did this was that he would have to eat the wet drywall. Stop the work before he goes any further. Wet drywall becomes weak and becomes a source for mold to grow on. Also if the drywall got wet, so did the insulation. Can't tell you about the fireplace,but evaporator coils get wet when they're working anyway. Do not let him get away with this. Good luck, Ron J.