A structure or use located in a critical dune area that is destroyed by fire, other than arson for which the owner is found to be responsible, or an act of nature, except for erosion, is exempt from the operation of this part or a zoning ordinance under this part for the purpose of rebuilding or replacing the structure or use, if the structure or use was lawful at the time it was constructed or commenced. A replacement structure and its use may differ from that which was destroyed if it does not exceed in size or scope that which was destroyed.