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. Such six-month period of abandonment may be discontinued only by 30 or more consecutive business days of operation. A legal nonconforming use shall be substantially destroyed if the cost to repair and replace the structure subject to such nonconforming use exceeds 50% of the current structural replacement value thereof. Where more than one legal nonconforming use is maintained upon a lot, all of such uses must be abandoned as aforesaid in order for the legal nonconforming uses to be extinguished. Any legal nonconforming use which shall have been extinguished as a result of abandonment or destruction as set forth herein may be reinstated as to structure and/or use within two years of extinguishment by special permit by the Board of Trustees.