don't need to remove the head to heli-coil, just go slow, and use lot of valsalin on the tap, then that a tube taped on a vacuum hose and stuck as much of the clippings out of the cylinder as possible if any fell off the greased tap then take a a long dowelwith a cotton tip with some vasalin and poak around the cylinder head to get anything thats left, put some sealer on the insert install it the use the seat tool and hit it with a hammer, let the sealer set up before you install the plug, use real heli-coil inserts not the cheap wire type ones.

but if it mashed the plug I don't know if it hurt the valves and or the piston, you could be opening a can of worms.