If a building or other structure containing a non-conforming use is damaged or destroyed by any means to the extent of 50% of more of its replacement value at the time, the building or other structure can be rebuilt or used thereafter only for a conforming use and in compliance with the provisions of the district in which it is located. In the event the damage or destruction is less then 50% of its replacement value, based upon prevailing costs, the building may then be restored to its original condition and the occupancy or use of the building may be continued which existed at the time of the partial destruction. In either event, restoration or repair of the building or other structure must be started within a period of six months from the date of damage or destruction, and diligently prosecuted to completion.