As to any contingent remainder or executory or other future interest held by the slayer subject to become vested in him or increased in any way for him upon the condition of the death of the decedent:
(1) If the interest would not have become vested or increased if he had predeceased the decedent, he shall be deemed to have so predeceased the decedent; but
(2) In any case, the interest shall not be vested or increased during the period of the life expectancy of the decedent.