Abandonment and destruction. Whenever a legal nonconforming use shall have been abandoned for a term of six months, or whenever the structure in which a legal nonconforming use is located is substantially destroyed, the land, building or structure in which said legal nonconforming use shall have existed shall not thereafter be used for any nonconforming use unless a special permit therefor shall have been received from the Board of Trustees. Such six-month period of abandonment may be discontinued only by 30 or more consecutive business days of operation. A structure in which a legal nonconforming use is located shall be substantially destroyed, if the cost to repair and replace the structure exceeds 50% of the current structural replacement value thereof.