I recently saw where a chimney had been removed from a roofline. How much demolition should have been done below the roofline and what measures should have been taken to ensure the fire places were never used again.

To close a chimney you don’t have to remove it at all. Just cap it at the top so no rain gets in and then close it off at the bottom in some fashion so that no one unknowingly tries to start a fire in the fireplace.