This chapter shall be effective only as to the property of residents of states which grant to property of residents of Alabama a similar exemption from death taxation. In the event, however, that such reciprocal provision contained in this section shall be declared unconstitutional or invalid, either in part or in whole, then Section 40-15-8 shall continue in full force and effect, it being the legislative intent to exempt the property described in Section 40-15-8 from death taxation notwithstanding any subsequent invalidation of the reciprocal provision herein contained.