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. There shall be no abandonment if, within the six-month term, the nonconforming use shall be reestablished for a period of at least 30 days. 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 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 within two years of extinguishment by special use permit by the Board of Trustees upon good use shown.