If any nonconforming building or structure shall be destroyed by reason of windstorm, fire, explosion or act of God or otherwise to an extent of more than partial destruction as provided for in N.J.S.A. 40:55D-68, then such destruction shall be deemed complete destruction, and the structure may not be rebuilt, restored or repaired, except in conformity with the regulations of this chapter. Nothing in this chapter shall prevent the strengthening or restoring to a safe condition of any wall, floor or roof which has been declared unsafe by the Construction Official.